Previously, settings for deployments of an ASP.NET application were stored in multiple configuration files under the Web.config config sections using a KEY/VALUE format. We are moving these 'site module options' to the database for a variety of reasons.
Here are the two options we are mulling over at the moment:
1. A single table with the applicationId, moduleId, and key as a Primary Key with a Value field.
Pros:
- This mimics the file access.
- It is easy to select entire sections to cache in hashtables/value objects.
Cons:
- More difficult to update since each key needs to be updated individually.
- Must cast each value if it's not a string.
2. Individual tables for each section which separate stored procedures, classes, etc.
Pros:
- Data is guaranteed to be consistent since the column and object types are typed.
- Updating is done in one trip to the database through an explicit interface.
Cons:
- Must change the application interface to access the
- Must update the objects, database tables, and stored procedures each time something changes.
Do either of these sound like good ideas or is there another way I may have overlooked?
If I understand what you are proposing correctly. I would do the first approach. It leverages what you have already built. I would use the hash tables for caching inside of wrapper classes that can provide stongly typed interfaces for the properties.
For example:
/// <summary>
/// The time passwords expire, in days, if ExpirePasswords is on
/// </summary>
public int PasswordExpirationDays {
get { return ParseUtils.ParseInt(this["PasswordExpirationDays"], PW_MAX_AGE);}
set { this["PasswordExpirationDays"] = value.ToString(); }
}
Another option is to group like settings together into their own classes, and then use XML serialization/deserialization to store and retrieve instances of these settings classes to and from the database.
This doesn't specifically provide advantages above and beyond a key/value pair other than you don't have to yourself perform any type conversions (this is done behind the scenes as part of the serialization/deserialization process - so it still does happen). I find this sort of approach ideally suited for solving configuration issues such as you are facing. Its clean, quick to implement, very easy to expand, and very easy to test. You don't have to spend time creating a feature rich API to get at your settings, especially if you've already got your configuration subclassed out.
Also in a pinch you can direct your settings to come from database tables or the file system without altering your serialization/deserialization code (this is very nice during development).
Finally if you are using SQL Server (and likely Oracle, though I have no experience with Oracle and XML) and you think about the design of your settings class up front, you can define an XML schema for your serialized configuration object instances so you can use XQuery to quickly get a configuration setting's value without having to fully deserialize.
This is how we did it - Click Here
We were more concerned with the fact that different environments (Dev, Test, QA and Prod), had different values for the same key. Now we have only 2 keys in a WebEnvironment.Config file that never gets promoted. The first key is which environment are you in and the second one is the connection string.
The table gets loaded up once to a dictionary and then we can use it in our code like this:
cApp.AppSettings["MySetting"];
Related
I have seen a particular pattern a few times over the last few years. Please let me describe it.
In the UI, each new record (e.g., new customers details) is stored on the form without saving to database. This clearly has been done so not clutter the database or cause unnecessary database hits.
While in the UI state, these objects are identified using a Guid. When these are a saved to the database, their associated Guids are not stored. Instead, they are assigned a database Int as their primary key.
The form can cope with a mixure of retrieved items from the database (using Int) as well as those that have not yet been committed (using Guid).
When inspecting the form (using Firebug) to see which key was used, we found a two part delimited combined key had been used. The first part is a guid (an empty guid if drawn from the database) and the second part is the integer (zero is stored if it is not drawn from the database). As one part of the combined key will always uniquely identify a record, it works rather well.
Is this Good practice or not? Can anyone tell me the pattern name or suggest one if it is not already named?
There are a couple patterns at play here.
Identity Field Pattern
Defined in P of EAA as "Saves a database ID field in an object to maintain identity between an in-memory object and a database row." This part is obvious.
Transaction Script and Metadata Mapping
In general, the ASP.NET DataBound controls use something like an Transaction Script pattern in conjunction with a Metadata Mapping pattern. Fowler defines Metadata Mapping as "holding details of object-relational mapping in metadata". If you have ever written a data source control, the Metadata Mapping aspect of this pattern seems obvious.
The Transaction Script pattern "organizes business logic by procedures where each procedure handles a single request from the presentation." In order to encapsulate the logic of maintaining both presentation state and data-state it is necessary for the intermediary object to indicate:
If a database record exists
How to identify the backend data record, to populate the UI control
How to identify the data and the UI control if there is no current data record, so that presentation data can be updated from the backend datastore.
The presence of the new client data entry Guid and the data-record integer Id provide adequate information to determine all of this with only a single call to the database. This could be accomplished by just using integers (and perhaps giving a unique negative integer for each unpersisted UI data item), but it is probably more explicit to have two separate fields.
Good or Bad Practice?
It depends. ASP.NET is a pretty successful software project, and this pattern seems to work consistently. However, this type of ASP.NET web control has a very specific scope of application - to encapsulate interaction between a UI and a database about data objects with simple mappings. The concerns do seem a little blurred, but for many applicable scenarios this will still be acceptable. The pattern is valid whereever a Row Data Gateway would be acceptable. If there is more than one database row affected by a web control, then this approach will not be functional. In these more complex cases, either an Active Record implementation or the combination of a Domain Model and a Repository implementation would be better suited.
Whether a pattern is good or bad practice really depends on the scenario in which it is being applied. It seems like people tend to advocate more complex design structures, because they can be applied to more scenarios without failing. However, in a very simple application where the mappings between data records and the UI are direct, this pattern is very useful because it creates the intended result while minimizing the amount of performance and development overhead.
I don't think there is a specific pattern for that.
Is it good practice? I don't think so. First, it's not very object oriented. How about:
interface ICommittable
{
/// <summary>
/// Gets or sets a value indicating whether the entity was already committed to the database.
/// </summary>
bool IsCommitted;
/// <summary>
/// Gets or sets the ID of the entity, used either in database or generated by UI or an underlying BL.
/// </summary>
Guid Id;
}
Instead, what they do is to mix three separate data entries in one in a non obvious way:
The ID
Another ID (why?)
A fact that the entity was committed or not.
Especially, having two separate IDs is extremely confusing and will require not only a good documentation, but some time for a new developer to understand what's happening here.
If the purpose was to create new entities without querying the database for a new ID, they could use GUIDs everywhere: when a new entity is created, you Guid.CreateNew it's ID, then, if need, you commit everything, this GUID being the identifier in the database too (there are few chances to have a collision between already saved GUIDs and a new one, so I wouldn't care about that).
Much more simple, isn't it?
It's also not easy to do a few things. For example, how do you compare two entities? Remember that:
Two committed entities which have different GUIDs are not equal,
Two not committed entities which have different IDs are not equal,
A committed entity may be equal to a non committed entity, even if their GUIDs and their IDs will be different.
To conclude, it seems like a lack of refactoring. Probably they were modifying a project where entities were already identified in the database by their id (int) unique key, so instead of refactoring this, they just added GUIDs, thus making the overall thing:
More difficult to understand,
Very difficult to work with and to modify in future.
If I'm not wrong it's the repository pattern: http://martinfowler.com/eaaCatalog/repository.html
This is well described in the Evans Domain Driven Design book and has proven to work well under specific circumstances.
I am developing a website for a client (ASP.NET, T-SQL). It is a data-entry website allowing many of their users to login and manipulate records in the same database.
There are instructions (basically a list of string) throughout the form, telling the users what to do for each section; these instructions are themselves present in the database.
On each login, I store these instructions in the Session[] object per authenticated user. The instructions are identical for everyone.
I've looked at a solution which suggested storing a common session identifier in the database and then querying it to re-use that particular session but this seems very hacky. What is a best-practices solution to accomplish this? Is there a 'common' object available to all users?
Firstly, does it matter at this point? Yes, it's bad practice and inefficent, but if you're storing 20Kb of strings in memory and have a maximum of 100 users, that's 2,000Kb of data. Hardly a lot of memory "wasted". Even at 200Kb of strings, that's 20,000Kb of data. Again, not a lot. Is it worth your time, and the client waiting for you to solve it, right now?
If you decide it is then you could:
Store the strings in the Application object or a static class so that they're retrieved once and used many times.
Retrieve the strings on every page view. This may not be as performance damaging as it seems.
Use something like the Cache class in System.Web.Caching.
Make use of Output Caching.
Make use of Windows Server AppFabric "Velocity" memory cache.
Sounds to me like you're looking for the Application Cache. Like the Session, it is an in-memory cache of data. Unlike the session, it is shared among all users; each user doesn't get their own individual copy of the data. Also, when you add data elements to the cache, you can specify criteria which will automatically invalidate that data, and cause it to be reloaded/refreshed (useful when your seldom-changing data actually does change :).
Here's some articles which should give you everything you need to know about using the Application cache (and some other caching options within ASP.NET as well):
ASP.NET Caching Overview
Using the ASP.NET Application Cache to Make Your Applications Scream
Caching Data at Application Startup
.NET Data Caching
I would suggest using the application-level Cache object. It is available everywhere as part of HttpContext. You can populate it on App_Start.
You can put any kind of object into Cache, though obviously, the smaller the better.
Here are some examples of how to populate it using C#:
1) Add items to the cache as you would add items to a dictionary by specifying the item's key & value.
Example: add the current Value property of a text box to the cache.
Cache["txt1"] = txtName.value;
or
Cache["result"] = dataset;
2) The Insert method is overloaded, allowing you to define values for the parameters of the version you're using.
Example: add only an item key & value:
Cache.Insert("MyData1", connectionString);
3) The Add method has the same signature as the Insert method, but it returns an object representing the item you added.
Cache.Add("MyData1", connectionString);
To retrieve the from cache:
stringName = Cache["MyData"];
If the cached data is not a string, you may need to cast it to the proper data type.
result = (DataSet)Cache["result"];
One of the benefits of using the Cache object as opposed to the Application object is that the CLR will dump contents of Cache if the system is in danger of running out of memory.
I need to store a few attributes of an authenticated user (I am using Membership API) and I need to make a choice between using Profiles or adding a new table with UserId as the PK. It appears that using Profiles is quick and needs less work upfront. However, I see the following downsides:
The profile values are squished into a single ntext column. At some point in the future, I will have SQL scripts that may update user's attributes. Querying a ntext column and trying to update a value sounds a little buggy to me.
If I choose to add a new user specific property and would like to assign a default for all the existing users, would it be possible?
My first impression has been that using profiles may cause maintainance headaches in the long run. Thoughts?
There was an article on MSDN (now on ASP.NET http://www.asp.net/downloads/sandbox/table-profile-provider-samples) that discusses how to make a Profile Table Provider. The idea is to store the Profile data in a table versus a row, making it easier to query with just SQL.
More onto that point, SQL Server 2005/2008 provides support for getting data via services and CLR code. You could conceivably access the Profile data via the API instead of the underlying tables directly.
As to point #2, you can set defaults to properties, and while this will not update other profiles immediately, the profile would be updated when next it is accessed.
Seems to me you have answered your own question. If your point 1 is likely to happen, then a SQL table is the only sensible option.
Check out this question...
ASP.NET built in user profile vs. old stile user class/tables
The first hint that the built-in profiles are badly designed is their use of delimited data in a relational database. There are a few cases that delimited data in a RDBMS makes sense, but this is definitely not one of them.
Unless you have a specific reason to use ASP.Net Profiles, I'd suggest you go with the separate tables instead.
What is the best way to design the Domain objects which can have multi-lingual fields. An example can be a Product class with Description being multi-lingual.
I have found few links but could not decide which one is the best way.
http://fabiomaulo.blogspot.com/2009/06/localized-property-with-nhibernate.html
(This stores all localised language data in one field. Can be a problem if we query from Sql)
http://ayende.com/Blog/archive/2006/12/26/LocalizingNHibernateContextualParameters.aspx
(This one has a warning at the beginning that it is a hack and no longer supported)
http://www.webdevbros.net/2009/06/24/create-a-multi-languaged-domain-model-with-nhibernate-and-c/
(This does not describe how multilingual data will be structured in the database.)
Anyone having experience with using NHibernate with multi-lingual data. Is there a better way?
The third option looks great. The hibernate mapping is given, but not the database schema - if that's what you are missing, then I'll sketch it out here:
dictionary
----------
ID: int - identity
name: nvarchar(255)
phrase
------
dictionary_id:int (fkey dictionary.ID)
culture_id:int (LCID)
phrase:nvarchar(255) - this is the default size - seems too small
According to this blog entry, 255 is the default string length for String values. To overcome the short string length on the phrase text, you can change the <element> tag to
<element column="phrase" type="String" length="4001"></element>
To use this in your domain model, you add a PhraseDictionary property to your entity where you want translatable text. E.g. the title property or decription property.
I think the article describes a great approach, and is the one that I would go
for.
EDIT: In response to the comments, make the length less than 4001 if you know the absolute maximum size is less than that, as this will typically be faster. Also, NHibernate will lazily fetch the collection, but it may fetch all the items at once. You can profile to determine if this has any performance implications. (If you have only a handful of languages then I doubt you will see a difference.) If you have many languages (Say 50+) then it may be worthwhile creating custom properties to fetch the localized text. These will issue queries to fetch specifically the text required. More importantly, you may be able to fetch all the text for a given entity in one query, rather than each localized text property as a separate query.
Note that this extra effort is only needed if profiling gives you reason to be concerned about the performance. Chances are that the implementation in the article as is will function more than adequately.
I only have experience for Hibernate, but since nHibernate is so similar:
One option is to define a component type MultilingualString with members for each language (this assumes the set of languages is known at coding time). This type is also a convenient location to place an getter for the string by language id.
class MultiLingualString {
String english;
String chinese;
String klingon;
String forLanguage(Language lang) {
switch (lang) {
// you can guess what goes here
}
}
}
This results in the strings for all languages being stored in separate columns in the database while the representation in the object world retains fine granularity.
The advantage is that no join is required to fetch the strings. On the other hand, the only way not to fetch a string with this approach is to use a projection, which is a severe limitation if the strings are large, numerous and rarely needed.
If you do this a lot, writing a UserType might be worth it.
From a strictly database oriented standpoint with SQL Server, you should have one table with all of the base data (record key, dates, numbers, etc) and one table with all of the translatable string data. Let call the two tables Base and Base_Description.
Base ensures that there is a single key for each record, the key might be a string or auto-generated id depending on your particular use case.
The Base_Description table is related to the Base table, but also contains a value to select the language that the data is in. In my projects we use the langid column from sys.languages because we can set the language of the connection with and then grab it with ##LANGID for most operations.
In our testing we found this to be significantly faster than having multiple fields for each language, it also allows you to add other languages more easily. We are also using SQL Server Full-Text indexing and it fully works with this method. You should index in the neutral language and then you can pick the language to search against at run time (also filtering against the LangID column in Base_Description).
Do your requirements include the domain objects actually having multiple-language properties in the same object? And, if so, is it unlimited translations stored in the object (in a collection, say - in which case I would say that it would need to be just like any master/detail or parent/child collection) or fixed translations, in which case the languages (and thus the mapping to results of a stored proc or whatever) have to be determined statically anyway?
In many internationalized applications I worked on, the data was in only one language - customer names, the product names (there was no point in mapping even identical products used in one country to products in another, they all had different distributors and different SKUs, and of course localized pricing). The interface was also only in one language (at a time). So all the domain objects only required one language at a time. Thus the language of the translation would be determined when the object was instantiated.
We had translation user interfaces which allowed users to update the translated texts, but these only required two languages at a time (local and the default). I can see this being closest to what you are talking about. I guess that you would have child collections for each translatable property with all the possible translations in the collection. This would probably be closest to the second solution in the third article you linked. Of course, at this point you would also need to see if you want eager/lazy loading etc.
For the sake of argument assume that I have a webform that allows a user to edit order details. User can perform the following functions:
Change shipping/payment details (all simple text/dropdowns)
Add/Remove/Edit products in the order - this is done with a grid
Add/Remove attachments
Products and attachments are stored in separate DB tables with foreign key to the order.
Entity Framework (4.0) is used as ORM.
I want to allow the users to make whatever changes they want to the order and only when they hit 'Save' do I want to commit the changes to the database. This is not a problem with textboxes/checkboxes etc. as I can just rely on ViewState to get the required information. However the grid is presenting a much larger problem for me as I can't figure out a nice and easy way to persist the changes the user made without committing the changes to the database. Storing the Order object tree in Session/ViewState is not really an option I'd like to go with as the objects could get very large.
So the question is - how can I go about preserving the changes the user made until ready to 'Save'.
Quick note - I have searched SO to try to find a solution, however all I found were suggestions to use Session and/or ViewState - both of which I would rather not use due to potential size of my object trees
If you have control over the schema of the database and the other applications that utilize order data, you could add a flag or status column to the orders table that differentiates between temporary and finalized orders. Then, you can simply store your intermediate changes to the database. There are other benefits as well; for example, a user that had a browser crash could return to the application and be able to resume the order process.
I think sticking to the database for storing data is the only reliable way to persist data, even temporary data. Using session state, control state, cookies, temporary files, etc., can introduce a lot of things that can go wrong, especially if your application resides in a web farm.
If using the Session is not your preferred solution, which is probably wise, the best possible solution would be to create your own temporary database tables (or as others have mentioned, add a temporary flag to your existing database tables) and persist the data there, storing a single identifier in the Session (or in a cookie) for later retrieval.
First, you may want to segregate your specific state management implementation into it's own class so that you don't have to replicate it throughout your systems.
Second, you may want to consider a hybrid approach - use session state (or cache) for a short time to avoid unnecessary trips to a DB or other external store. After some amount of inactivity, write the cached state out to disk or DB. The simplest way to do this, is to serialize your objects to text (using either serialization or a library like proto-buffers). This helps allow you to avoid creating redundant or duplicate data structure to capture the in-progress data relationally. If you don't need to query the content of this data - it's a reasonable approach.
As an aside, in the database world, the problem you describe is called a long running transaction. You essentially want to avoid making changes to the data until you reach a user-defined commit point. There are techniques you can use in the database layer, like hypothetical views and instead-of triggers to encapsulate the behavior that you aren't actually committing the change. The data is in the DB (in the real tables), but is only visible to the user operating on it. This is probably a more complicated implementation than you may be willing to undertake, and requires intrusive changes to your persistence layer and data model - but allows the application to be ignorant of the issue.
Have you considered storing the information in a JavaScript object and then sending that information to your server once the user hits save?
Use domain events to capture the users actions and then replay those actions over the snapshot of the order model ( effectively the current state of the order before the user started changing it).
Store each change as a series of events e.g. UserChangedShippingAddress, UserAlteredLineItem, UserDeletedLineItem, UserAddedLineItem.
These events can be saved after each postback and only need a link to the related order. Rebuilding the current state of the order is then as simple as replaying the events over the currently stored order objects.
When the user clicks save, you can replay the events and persist the updated order model to the database.
You are using the database - no session or viewstate is required therefore you can significantly reduce page-weight and server memory load at the expense of some page performance ( if you choose to rebuild the model on each postback ).
Maintenance is incredibly simple as due to the ease with which you can implement domain object, automated testing is easily used to ensure the system behaves as you expect it to (while also documenting your intentions for other developers).
Because you are leveraging the database, the solution scales well across multiple web servers.
Using this approach does not require any alterations to your existing domain model, therefore the impact on existing code is minimal. Biggest downside is getting your head around the concept of domain events and how they are used and abused =)
This is effectively the same approach as described by Freddy Rios, with a little more detail about how and some nice keyword for you to search with =)
http://jasondentler.com/blog/2009/11/simple-domain-events/ and http://www.udidahan.com/2009/06/14/domain-events-salvation/ are some good background reading about domain events. You may also want to read up on event sourcing as this is essentially what you would be doing ( snapshot object, record events, replay events, snapshot object again).
how about serializing your Domain object (contents of your grid/shopping cart) to JSON and storing it in a hidden variable ? Scottgu has a nice article on how to serialize objects to JSON. Scalable across a server farm and guess it would not add much payload to your page. May be you can write your own JSON serializer to do a "compact serialization" (you would not need product name,product ID, SKU id, etc, may be you can just "serialize" productID and quantity)
Have you considered using a User Profile? .Net comes with SqlProfileProvider right out of the box. This would allow you to, for each user, grab their profile and save the temporary data as a variable off in the profile. Unfortunately, I think this does require your "Order" to be serializable, but I believe all of the options except Session thus far would require the same.
The advantage of this is it would persist through crashes, sessions, server down time, etc and it's fairly easy to set up. Here's a site that runs through an example. Once you set it up, you may also find it useful for storing other user information such as preferences, favorites, watched items, etc.
You should be able to create a temp file and serialize the object to that, then save only the temp file name to the viewstate. Once they successfully save the record back to the database then you could remove the temp file.
Single server: serialize to the filesystem. This also allows you to let the user resume later.
Multiple server: serialize it but store the serialized value in the db.
This is something that's for that specific user, so when you persist it to the db you don't really need all the relational stuff for it.
Alternatively, if the set of data is v. large and the amount of changes is usually small, you can store the history of changes done by the user instead. With this you can also show the change history + support undo.
2 approaches - create a complex AJAX application that stores everything on the client and only submits the entire package of changes to the server. I did this once a few years ago with moderate success. The applicaiton is not something I would want to maintain though. You have a hard time syncing your client code with your server code and passing fields that are added/deleted/changed is nightmarish.
2nd approach is to store changes in the data base in a temp table or "pending" mode. Advantage is your code is more maintainable. Disadvantage is you have to have a way to clean up abandonded changes due to session timeout, power failures, other crashes. I would take this approach for any new development. You can have separate tables for "pending" and "committed" changes that opens up a whole new level of features you can add. What if? What changed? etc.
I would go for viewstate, regardless of what you've said before. If you only store the stuff you need, like { id: XX, numberOfProducts: 3 }, and ditch every item that is not selected by the user at this point; the viewstate size will hardly be an issue as long as you aren't storing the whole object tree.
When storing attachments, put them in a temporary storing location, and reference the filename in your viewstate. You can have a scheduled task that cleans the temp folder for every file that was last saved over 1 day ago or something.
This is basically the approach we use for storing information when users are adding floorplan information and attachments in our backend.
Are the end-users internal or external clients? If your clients are internal users, it may be worthwhile to look at an alternate set of technologies. Instead of webforms, consider using a platform like Silverlight and implementing a rich GUI there.
You could then store complex business objects within the applet, provide persistant "in progress" edit tracking across multiple sessions via offline storage and easily integrate with back-end services that providing saving / processing of the finalised order. All whilst maintaining access via the web (albeit closing out most *nix clients).
Alternatives include Adobe Flex or AJAX, depending on resources and needs.
How large do you consider large? If you are talking sessions-state (so it doesn't go back/fore to the actual user, like view-state) then state is often a pretty good option. Everything except the in-process state provider uses serialization, but you can influence how it is serialized. For example, I would tend to create a local model that represents just the state I care about (plus any id/rowversion information) for that operation (rather than the full domain entities, which may have extra overhead).
To reduce the serialization overhead further, I would consider using something like protobuf-net; this can be used as the implementation for ISerializable, allowing very light-weight serialized objects (generally much smaller than BinaryFormatter, XmlSerializer, etc), that are cheap to reconstruct at page requests.
When the page is finally saved, I would update my domain entities from the local model and submit the changes.
For info, to use a protobuf-net attributed object with the state serializers (typically BinaryFormatter), you can use:
// a simple, sessions-state friendly light-weight UI model object
[ProtoContract]
public class MyType {
[ProtoMember(1)]
public int Id {get;set;}
[ProtoMember(2)]
public string Name {get;set;}
[ProtoMember(3)]
public double Value {get;set;}
// etc
void ISerializable.GetObjectData(
SerializationInfo info,StreamingContext context)
{
Serializer.Serialize(info, this);
}
public MyType() {} // default constructor
protected MyType(SerializationInfo info, StreamingContext context)
{
Serializer.Merge(info, this);
}
}