I have a question regarding mapping and entities/domains with Flex/Spring mapping via BDS. I currently have domains mapped to tables, and I am working off existing code to try and change the logic from web services to work with Blaze.
Now, i came across a value object used previously that mapped to a datagrid, but that value object wasnt a true table entity. Now I split that value object into two logical ones, MessageItemFormats and MessageItemTypes. Now, that it is split, i have to find a way to work with both of them at the same time. I have a datagrid in the view that maps as a dataProvider to the valueObject. How do I map it to a split set of domains?
I am new to hibernate/Java, so I am not sure how this works from the Flex site of things... How do I join them to get attributes from both entities?
Related
I have a use case where DynamoDB is running in production and I need to add a new column IDUpdatedAt which will also be serving as a sort key for one of the GSIs.
I tried a thing in test where my application adds the new rows with IDUpdatedAt, it's working fine but what about the existing rows? How to add the values for those?
Also the new rows will not be added without IDUpdatedAt, but how will the search be impacted for older rows?
PS: IDUpdatedAt is being used as a filter in the application, i.e., user can search for specific ID and can get results sorted by date. That's why IDUpdatedAt is also a part of GSI (sort key).
Please help.
You've got the right idea by adding the field to new items. After all, DynamoDB does not enforce a particular schema outside of the primary key.
This also happens to be a very useful feature, especially when defining a GSI on that attribute; if the atttibute exists on the item, it ends up in the index! For example, imagine modeling an email inbox in DDB where each item represents an email. You could include an attribute 'is_read' and define a GSI using that atttibute.
If the 'is_read' attribute exists on the item, it's in the index. Otherwise, it's not. A cool way to use GSIs to implement filtering.
Pretty neat stuff!
However, there is no way to retroactively update all items with a new attribute other than manually updating each item (or in batches). The equivalent in SQL databases is defining a new column. Unfortunately, an analogous operation in DDB does not exist.
I am working on an enterprise scale project where I have a self referencing table called categories as below. Also in my current model I am using following table associations to fetch data. ( using EF6).
I have M-M mapping tables in DB for above M-M relationships.
In my controller GET action result returns the model which has Ilist(all parent categories). Then when the user is selecting items (in view) I am using Ajax to retrieve Ilist for next subset of categories (by passing to controller by Id - return Json result) and dynamically show next to the parent select list as below. ( and I have up to 4 subsets)
As the user is selecting categories, I am using Ajax call to load related categories and create selectlist or dropdownlist dynamically as below:
My question is Since all these data is loaded through Ajax, how can I bind them to my parent model. How can I capture user selected data into one parent model when user is posting the from to controller.
I know I can use Ajax and use Json to capture & transfer to contoller , But I need to use modelview , Can I use partiview to overcome this ?
Please advise the available options..
The key is making sure the name values match the object hierarchy accepted by the post operation. This is certainly doable; it's difficult because several AJAX operations build the UI, but one operation processes it, so you have to ensure the data expressions match the object being posted back.
You can use Html.NameFor() as a workaround to ensuring the naming paths work OK. Collections can make this difficult.
My team is evaluating JavaFX as a platform for a database application which will make intense use of TableViews. We are under impression that in order to display data in tables we will have to sub-class TableView and write our own ValueFactory classes for each column data type and presentation mode we are going to need.
For example if we wanted to display bit fields as Yes/No text and on/off checkboxes, we would need 2 ValueFactories or one ValueFactory and two CellFactories for bit data type.
Q1: Is our understanding correct?
Q2: Do any 3d party libraries exist that would allow us to simply set a data binding property of their version of TableView to a ResultSet for example and automatically display data with minor tweaking of display mode?
As evaluation goes on there are more questions arising.
Q3: Willl we have to create a data row class for every SQL query and ObservableList for every class, which would mean that every time we changed returned columns, we would have to re-write data row class? Would we have to implement paging by keeping resultsets in memory and re-populating the ObservableLists on scrolling too?
Q1 - For each column you should specify valueFactory - very easy. If you don't want to show value as default you can specify cellfactory - not so easy. I think best practice is create own class which will extends TableView and you will specify everything you need. You can also create your own TableCell classes etc. I think this work is not so hard in developing javafx app.
Q2 - I don't know but i would create own classes.
Q3 - Observablelist should contain your entity class. Each query should return list of entity objects. Value factory is link with some entity object property.
I have a stored procedure that search a view using full text.
I'm trying to map the results to an existing Entity (Sales), where I mapped the column MivType to SaleType (as it makes more sense, and I want to keep db names away from my web site). The stored procedure is mapped to a Function Import, and I've defined its ReturnType to Sales.
This work well as long as the entity has the same property names as fields names.
Here's my problem: when I change the property's name, I get the following error after running the imported function:
The data reader is incompatible with the specified 'Model.Sale'. A member of the type, 'SaleType', does not have a corresponding column in the data reader with the same name.
I can fix this if I change the property 'SaleType' to 'MivType' on the entity, but why should I do that? Isn't that what the mapping is for?
This means I have to use the exact same names on the stored procedure and the entity, so in effect, the mapping is ignored (I have names like YzrName, MivYaad, etc, and I don't like it).
Is there a simple way around this? I don't want to use the db names on my application, and prefer not to change the stored procedure...
(I should mention I'm a beginner with the EF, so this can be a rookie mistake)
Thanks.
Well the entity designer doesnt work very well. I generally try to do everything in the XML. In the XML there are 3 parts. The Storage (a representation of the SQL Database). The Conceptual (a represention of your .Net Objects. and the Conceptual to Storage Mapping
It sounds like the error is in your Conceptual to Storage Mapping. You can keep the property name SalesType on the conceptual side but the mapping must map the the correct names on both the conceptual and storage side.
Refer to MSDN here are some articles
http://msdn.microsoft.com/en-us/library/cc716731.aspx
Often I need to combine data from multiple tables and display the result in a GridView control.
I can write a Linq query inline in the Page_load event, return an anonymous type that combines all the fields that I need, and databind the result to the GridView control.
Problem: I use 'helper methods' as described by Scott Guthrie on his blog. Such a helper method cannot return an anonymous type. The query would have to be inline for this approach.
I can write a database view that returns the data that I need, and write a helper method with a query against this (new and known) type that it returns.
Problem: I will need a lot of views in my database schema, and I will introduce a lot of redundant aspects of my data. I also lose some of the advantage of using Linq - removing all business logic from the database.
I would like to take an approach that lets me keep the Linq queries in helper methods, yet allows me to access all the attributes that I need on the grid in their respective databinding expressions. Can this be done?
I asked the wrong question, as I frequently do. What prompted me to look into anonymous types was an apparent limitation of the GridView - my inability to use a databinding expression in an <asp:BoundField> (the DataField parameter only accepts column names of the table that the Linq query pulls in).
Turns out that in a TemplateField it is possible to use Eval and access members of the Linq data item, and Linq takes care of the query for me.
In other words, I can keep the query in my helper method, have it return a primary database table type (e.g. Account), and I bind the Accounts to the GridView.
In the databinding expressions I can access data members of the Account objects that reside in other tables, without having to explicitly pull them in in the query. Perfect.
I don't know if there is a viable way to achieve this using anonymous types. But I have a suggestion that will work in WinForms, but I am not sure about ASP.NET.
What you need is a type with properties where neither the number of properties, nor the types and names of the properties are known at compile time. One way to create such a thing is ICustomTypeDescriptor.
You have to create a type implementing this interface with an private backing store of objects backing the properties returned by the query for one row from the query. Then you implement GetProperties() to return one PropertyDescriptor per column and PropertyDescriptor.GetValue() and PropertyDescriptor.SetValue() to access the backing array.
By implementing PropertyDescriptor.Name you will get the correct column name; this will probably require another backing store storing the property names. And there is a lot more to implement, but in the end your new type will behave almost like a normal type - and now the if - if the control you are binding to knows about and uses ICustomTypeDescriptor.
UPDATE
I just found an bit of text stating that ASP.NET data binding knows and uses ICustomTypeDescriptor.
Scott's earlier post in the series talks about shaping the result set before inserting into a grid:
Part 3 - Querying our Database
Scroll down to "Shaping our Query Results".