So I've implemented objectDataSource custom paging in the DAL using stored proceedures like all the guides and tutorials describe, but I'm realizing that by putting your custom paging logic at the data access layer, you are limited on how much you can use your Domain model.
For instance, I have a webform with a gridview that I want to display every Customer (CustomerId) that's belongs to a specific Office (OfficeId) and the status of their Order (OrderId) if they have one.
So in my services layer I could fill a DTO list like (I'm a newbie when it comes to DDD so I'm sure this design isn't great but bear with me):
ObjectDataSource SelectMethod tied to:
public List<CustomerAndOrderDTO> GetCustomersByOffice(int officeId, int startPageIndex, int maxiumRows)
{
List<CustomerAndOrderDTO> customerAndOrderDTO = null;
List<Customer> customers = Customer.GetCustomersByOffice(int officeId);
foreach (Customer customer in customers)
{
customerAndOrderDTO.Add(new CustomerAndOrderDTO(customer));
}
return customerAndOrderDTO;
}
And this is the DTO class:
public CustomerAndOrderDTO
{
public int OrderId {get; set;}
public int CustomerId {get; set;}
public CustomerAndOrderDTO(Customer customer)
{
CustomerId = customer.Id;
Order order = customer.GetOrder();
OrderId = order.Id;
}
}
Pretty simple code and you get all the flexibility and power of the domain model plus validation and persistence checking while staying in the BLL.
Even if you wanted to ignore the benefits of aggregating your objects in the domain and just combine the data at the stored procedure level like select * from Customers left join Orders on .... left join Office on ... where.... you'd end up writing a million extension methods that implement paging for every possible combination like CustomersOrdersByOfficePaged, CustomersOrdersByAccountDatePaged, etc...
So am I just doing it wrong to begin with? Or does paging at the Service layer make sense? If so, how does one implement it?
So, I'm sure, big picture-wise, this isn't the best architecture, but to implement paging at the service level you can just query your objects from the data access level and then implement the paging logic on your object list at your BLL level like so:
if ((startRowIndex != 0 && startRowIndex != null)
&& (maximumRows != 0 && maximumRows != null))
{
if ((audits.Count - startRowIndex) < maximumRows)
{
audits = audits.GetRange((int)startRowIndex, audits.Count - (int)startRowIndex);
}
else
{
audits = audits.GetRange((int)startRowIndex, (int)maximumRows);
}
}
return audits;
The Count method required by the objectDataSource takes the same parameters as your main "Get" method and calls that "Get" method and then returns the .Count.
Again, not the best way but gets the job done.
Have a look at Dynamic LINQ.
This should help you out:
ScottGu's Blog - Dynamic LINQ
CodeProject's Dynamic Querying with LINQ-to-Entities and
Expressions
Stack Overflow question - Dynamic LINQ OrderBy
Joe Stevens' LINQ to SQL tutorial objectDataSource binding with paging
and sorting
I hope this helps!
Related
To make updates to a record of SQL Server using Entity Framework Core, I query the record I need to update, make changes to the object and then call .SaveChanges(). This works nice and clean.
For example:
var emp = _context.Employee.FirstOrDefault(item => item.IdEmployee == Data.IdEmployee);
emp.IdPosition = Data.IdPosition;
await _context.SaveChangesAsync();
But is there a standard method if I want to update multiple records?
My first approach was using a list passing it to the controller, but then I would need to go through that list and save changes every time, never really finished this option as I regarded it as not optimal.
For now what I do is instead of passing a list to the controller, I pass each object to the controller using a for. (kind of the same...)
for(int i = 0; i < ObjectList.Count; i ++)
{
/* Some code */
var httpResponseObject = await MyRepositories.Post<Object>(url+"/Controller", Object);
}
And then do the same thing on the controller as before, when updating only one record, for each of the records...
I don't feel this is the best possible approach, but I haven't found another way, yet.
What would be the optimal way of doing this?
Your question has nothing to do with Blazor... However, I'm not sure I understand what is the issue. When you call the SaveChangesAsync method, all changes in your context are committed to the database. You don't have to pass one object at a time...You can pass a list of objects
Hope this helps...
Updating records in bulk using Entity Framework or other Object Relational Mapping (ORM) libraries is a common challenge because they will run an UPDATE command for every record. You could try using Entity Framework Plus, which is an extension to do bulk updates.
If updating multiple records with a single call is critical for you, I would recommend just writing a stored procedure and call if from your service. Entity Framework can also run direct queries and stored procedures.
It looks like the user makes some changes and then a save action needs to persist multiple records at the same time. You could trigger multiple AJAX calls—or, if you need, just one.
What I would do is create an endpoint—with an API controller and an action—that's specific to your needs. For example, to update the position of records in a table:
Controller:
/DataOrder
Action:
[HttpPut]
public async void Update([FromBody] DataChanges changes)
{
foreach(var change in changes)
{
var dbRecord = _context.Employees.Find(change.RecordId);
dbRecord.IdPosition = change.Position;
}
_context.SaveChanges();
}
public class DataChanges
{
public List<DataChange> Items {get;set;}
public DataChangesWrapper()
{
Items = new List<DataChange>();
}
}
public class DataChange
{
public int RecordId {get;set;}
public int Position {get;set;}
}
The foreach statement will execute an UPDATE for every record. If you want a single database call, however, you can write a SQL query or have a stored procedure in the database and pass the data as a DataTable parameter instead.
I need to load multiple entity types in my View page. I am using ViewModel for this purpose. However, I need to make around 5-6 database calls to load each set of data and assign them to the relevant property of the ViewModel. I wonder if this is a recommended approach since it requires multiple database calls. Or, am I being over-concerned about this? Here is a snapshot from my code:
var model = new EntryListVM();
string userid = "";
if (ViewBag.CurrentUserId == null)
userid = User.Identity.GetUserId();
else
userid = ViewBag.CurrentUserId;
ViewBag.CurrentUserId = userid;
//First database call
model.DiscussionWall = db.DiscussionWalls.Find(wallId);
//Second database call to learn if the current students has any entry
model.DiscussionWall.DoesStudentHasEntry = db.Entries.Any(ent => ent.DiscussionWallId == wallId && ent.UserId == userid);
model.PageIndex = pageIndex;
//Third database call
model.TeacherBadges = db.Badges.Where(b => b.CourseId == model.DiscussionWall.CourseId && b.IsSystemBadge == false && b.IsEnabled == true).ToList();
//Fourth database call
model.Reactions = db.Reactions.Where(re => re.CourseId == model.DiscussionWall.CourseId).ToList();
int entryPageSize = Convert.ToInt32(ConfigurationManager.AppSettings["EntryPageSize"]);
int firstChildSize = Convert.ToInt32(ConfigurationManager.AppSettings["FirstChildSize"]);
List<ViewEntryRecord> entryviews = new List<ViewEntryRecord>();
bool constrainedToGroup = false;
if (!User.IsInRole("Instructor") && model.DiscussionWall.ConstrainedToGroups)
{
constrainedToGroup = true;
}
//Fifth database call USING VIEWS
//I used views here because of paginating also to bring the first
//two descendants of every entry
entryviews = db.Database.SqlQuery<ViewEntryRecord>("DECLARE #return_value int;EXEC #return_value = [dbo].[FetchMainEntries] #PageIndex = {0}, #PageSize = {1}, #DiscussionWallId = {2}, #ChildSize={3}, #UserId={4}, #ConstrainedToGroup={5};SELECT 'Return Value' = #return_value;", pageIndex, entryPageSize, wallId, firstChildSize, userid, constrainedToGroup).ToList();
model.Entries = new List<Entry>();
//THIS FUNCTION MAP entryviews to POCO classes
model.Entries = ControllerUtility.ConvertQueryResultsToEntryList(entryviews);
//Sixth database call
var user = db.Users.Single(u => u.Id == userid);
model.User = user;
I wonder if this is too much of a burden for the initial page load?
I could use SQL-View to read all data at once, but I guess I would get a too complicated data set to manage.
Another option could be using Ajax to load the additional results after the page loading (with the main data) is completed. For example, I could load TeacherBadges with AJAX after the page is being loaded.
I wonder which strategy is more effective and recommended? Are there specific cases when a particular strategy could be more useful?
Thanks!
It all depends on your scenario - different scenarios have different ways of doing things. There is no single right way of doing things that are similar in nature. What might work for me might not work for you. Ever heard that saying: there are many ways to kill a cat? Well this certainly applies to programming.
I am going to answer based on what I think you are asking. Your questions are very broad and not that specific.
However, I am not sure if this is a recommended approach since it
requires multiple database calls.
Sometimes you need to do one database call to get data, and sometimes you need to do more than one database call to get the data. For example:
User details with addresses: one call for user and one call for addresses
User details: one call
I am using ViewModel for this purpose.
Using view models for your views is a good thing. If you want to read up more on what I had to say about view models then you can go and read an answer that I gave on the topic:
What is ViewModel in MVC?
View models are ideal for when you have data that is coming from multiple datasets. View models can also be used to display data coming from one dataset, for example:
Displaying user details with multiple addresses
Displaying only user details
I read the data in the controller in separate linq statements, and
assign them to the relevant List property of the ViewModel.
I would not always return a list - it all depends on what you need.
If I have a single object to return then I will populate a single object:
User user = userRepository.GetById(userId);
If I have a list of objects to return then I will return a list of objects:
List<User> users = userRepository.GetAll();
It is of no use to return a single object and then to populate a list for this object:
List<User> user = userRepository.GetByUserId(userId).ToList();
Second option could be using SQL-View to read all data with one
database call, and then map them to the entities properly in
controller.
This is similar to your first question, how you return your data on the database level is up to you. It can be stored procedures or views. I personally prefer stored procedures. I have never used views before. Irrespective of what you choose your above mentioned repository methods should still look the same.
Third option could be using Ajax to load the additional results after
the page loading (with the main data) is completed.
You can do this if you want to. I would not do it if it is not really needed. I try to load data on page load. I try to get as much data on the screen before the page is fully loaded. There have been times that I had to go the AJAX route after the page was loaded. After the page was loaded I had to do an AJAX call to load my HTML table.
If you really just need to have data displayed then do just that. You do not need any fancy ways of doing this. Maybe later you need to change on screen data, then AJAX is cool to use.
I wonder which strategy is more effective and recommended? Are there
specific cases when a particular strategy could be more useful?
Let us say you want to display a list of users. We do a database call and return the list to the view. I do not normally use view models if I only return a list:
public class UserController : Controller
{
private IUserRepository userRepository;
private IAddressRepository addressRepository;
public UserController(IUserRepository userRepository, IAddressRepository addressRepository)
{
this.userRepository = userRepository;
this.addressRepository = addressRepository;
}
public ActionResult Index()
{
List<User> users = userRepository.GetAll();
return View(users);
}
}
And your view could look like this:
#model List<YourProject.Models.User>
#if (Model.Count > 0)
{
foreach (var user in Model)
{
<div>#user.Name</div>
}
}
If you need to get a single user's details and a list of addresses, then I will make use of a view model because now I need to display data coming from multiple datasets. So a user view model can look something like this:
public class UserViewModel
{
public UserViewModel()
{
Addresses = new List<Address>();
}
public int Id { get; set; }
public string Name { get; set; }
public List<Address> Addresses { get; set; }
}
The your details action method could look like this:
public ActionResult Details(int id)
{
User user = userRepository.GetById(id);
UserViewModel model = new UserViewModel();
model.Name = user.Name;
model.Addresses = addressRepository.GetByUserId(id);
return View(model);
}
And then you need to display the user details and addresses in the view:
#model YourProject.ViewModels.UserViewModel
<div>First Name: #Model.Name</div>
<div>
#if (Model.Addresses.Count > 0)
{
foreach (var address in Model.Address)
{
<div>#address.Line1</div>
<div>#address.Line2</div>
<div>#address.Line3</div>
<div>#address.PostalCode</div>
}
}
</div>
I hope this helps. It might be to broad of an answer but it can guide you on the correct path.
Includes for linked data
For linked data it's simple (you probably know this way):
var users = context.Users.Include(user => user.Settings).ToList();
It queries all users and pre-loads Settings for each user.
Use anonymous class for different data sets
Here is an example:
context.Users.Select(user => new
{
User = user,
Settings = context.Settings
.Where(setting => setting.UserId == user.Id)
.ToList()
}).ToList();
You still kinda need to choose your main query collection (Users in this case), but it's an option. Hope it helps.
My scenario:
This is an ASP.NET 4.0 web app programmed via C#
I implement a repository pattern. My repositorys all share the same ObjectContext, which is stored in httpContext.Items. Each repository creates a new ObjectSet of type E. Heres some code from my repository:
public class Repository<E> : IRepository<E>, IDisposable
where E : class
{
private DataModelContainer _context = ContextHelper<DataModelContainer>.GetCurrentContext();
private IObjectSet<E> _objectSet;
private IObjectSet<E> objectSet
{
get
{
if (_objectSet == null)
{
_objectSet = this._context.CreateObjectSet<E>();
}
return _objectSet;
}
}
public IQueryable<E> GetQuery()
{
return objectSet;
}
Lets say I have 2 repositorys, 1 for states and 1 for countrys and want to create a linq query against both. Note that I use POCO classes with the entity framework. State and Country are 2 of these POCO classes.
Repository stateRepo = new Repository<State>();
Repository countryRepo = new Repository<Country>();
IEnumerable<State> states = (from s in _stateRepo.GetQuery()
join c in _countryRepo.GetQuery() on s.countryID equals c.countryID
select s).ToList();
Debug.WriteLine(states.First().Country.country)
essentially, I want to retrieve the state and the related country entity. The query only returns the state data... and I get a null argument exception on the Debug.WriteLine
LazyLoading is disabled in my .edmx... thats the way I want it.
You're doing a join without retrieving anything from it. There are multiple solutions to your problem:
Use Include to load the dependent entities: from s in ((ObjectSet<State>) _stateRepo.GetQuery).Include("Country"). The problem with this approach is that you should expose the ObjectSet directly rather than as a IQueryable if you want to avoid casting.
Use context.LoadProperty(states.First(), s => s.Country) to explicitly load the Country from the database for a given state.
Select both entities in the query: from s in ... join c ... select new { s, c }. You won't be able to access directly the state's Country property but you have it in the anonymous type.
Enable lazy loading.
Your repository implementation is very similar to mine, especially the way you are storing the ObjectContext. It works fine for me, so I don't think it's a conceptual problem.
Try using a static objectcontext (no wrapper) just to see if that fixes the problem. Perhaps there is a bug in your ContextHelper which causes your context to get disposed and recreated.
I have some e-commerce code that I use often that uses Linq To SQL for saving orders to the database. I want to remove the tightly coupled Linq to SQL bit and pass in an IRepository instead but I am still a little confused on things.
Say I have a GetCustomer() method on my ICustomerRepository that returns a Customer object.
Do I need it to really return an ICustomer object that gets passed back from that method so if I switch from Linq To SQL to say SubSonic it's not a problem?
I believe I do, if that is the case is there a way in Linq To SQL to easily convert my Linq To SQL Customer object to my ICustomer object like SubSonics ExecuteSingle(Of ) method?
If you want your Customer class to be a plain object with no attachment to LINQ, then you will most likely need to write a mapper method to convert your LINQ-based Customer object to your plain Customer domain object. LINQ to SQL does not have such functionality built-in.
I have begun to wrap my mapping methods in an extension method for readability, and it really helps to keep the Repository code simple. For instance, an example CustomerRepository method my look like:
public Customer GetById(int id)
{
return dataContext.LINQCustomers.Where(c => c.Id == id)
.Single()
.ToDomainObject();
}
and the ToDomainObject() method is defined in an extension method like:
public static class ObjectMapper
{
public static Customer ToDomainObject(this Customer linqObject)
{
var domainObject = null
if (linqObject != null)
{
domainObject = new Customer
{
Id = linqObject.Id,
FirstName = linqObject.FirstName,
LastName = linqObject.LastName
}
}
return domainObject;
}
}
or something similar. You can do the same to convert your domain object back to a LINQ object to pass back into your repository for persistence.
You can have it return a Customer as long as Customer is a plain old .NET object, and not some db-generated entity. Your Customer domain object should have no knowledge about how (or if) it might be persisted to a database, and this is what should be returned from your repository. In your repository you might have some mapping code - this is quite common - that maps from [however you get the data back from its storage location] to your domain object. If you're using Linq-to-sql then this mapping would be from the Linq-To-Sql generated Customer table (and perhaps other tables - your Customer domain object likely won't map 1:1 to a particular table in the database) to your Customer domain object, which would live in a different namespace (and most likely, assembly).
There is no need to make it an ICustomer at all. A repository acts in a way as to make it look as though your persistent instances are in memory.
public interface ICustomerRepository
{
Customer GetByID(int id);
IEnumerable<Customer> GetByName(string name);
Customer GetByVatCode(string vatCode);
}
Some people would additionally include methods such as
void Add(Customer newCustomer);
void Delete(Customer deleted);
void Update(Customer modified);
The latter method implementations would most likely just update a unit of work.
The concept though is that these are just common ways of asking for Customer instances, the repository acts as a way of asking for them without defining how to ask for them.
What is difference to the controller that gets the return with repect to rendering the List?
In Linq dataContext:
public IList<Response> GetResponses(int ID)
{
var responses = from r in this.Responses where r.ID == ID orderby r.Date select r;
return responses.ToList();
}
OR
public List<Response> GetResponses(int ID)
{
var responses = from r in this.Responses where r.ID == ID orderby r.Date select r;
return responses.ToList();
}
I doubt there's much difference to the controller but you should probably try to reveal as little information as possible about the private data of your classes. This means exposing interfaces rather than concrete types and using the interface that exposes the minimum amount of information the client will need to operate on the data.
If the controller only needs an IEnumerable<Response> then you should consider making that the return type of GetResponses.
The difference is that the controller won't need to be updated if you change your List implementation if you use the IList interface. It's probably not that big of a deal unless you are planning to make your library available to others. In that case the abstraction is probably justified as you won't be the only one having to update your code if you make the change.
Consider returning an array, consider accepting IEnumerable as a parameter.