I have an object that has been populated with the contents of four different related entities. However i have another entity in which i cannot include as part of the query due to it not being related in the navigation properites directly to the IQueryable table i am pulling. The entity i am trying to include is related to one of the four different entities that have been included successfully.
Is there a way to include(during db hit or afterwards) this entity as part of the overall object i am creating?
Here is an example of what my calls look like to build the CARTITEM object:
public List<CARTITEM> ListCartItem(Guid cartId)
{
//Create the Entity object
List<CARTITEM> itemInfo = null;
using (Entities webStoreContext = new Entities())
{
//Invoke the query
itemInfo = WebStoreDelegates.selectCartItems.Invoke(webStoreContext).ByCartID(cartId).ToList();
}
//Return the result set
return itemInfo;
}
here is the selectCartItems filter(Where i would normally do the includes):
public static Func<Entities, IQueryable<CARTITEM>> selectCartItems =
CompiledQuery.Compile<Entities, IQueryable<CARTITEM>>(
(cart) => from c in cart.CARTITEM.Include("ITEM").Include("SHIPPINGOPTION").Include("RELATEDITEM").Include("PROMOTION")
select c);
from this i have my CARTITEM object. Problem is i want to include the PROMOTIONTYPE table in this object, but since the CARTIEM entity doesn't have a navigation property directly to the PROMOTIONTYPE table i get an error.
Let me know if you need any more clarification.
Thanks,
Billy
You can use join and if it is the same database and server it should generate the join in SQL and do it all in one call...
LinqToEnties join example
Related
I have a GridView which needs to page and sort data which comes from a collection of Customer objects.
Unfortunately my customer information is stored separately...the customer information is stored as a Customer ID in my database, and the Customer Name in a separate DLL.
I retrieve the ID from the database using Entity Framework, and the name from the external DLL through a partial class.
I am getting the ID from my database as follows:
public class DAL
{
public IEnumberable<Customer> GetCustomers()
{
Entities entities = new Entities();
var customers = (from c in entities.Customers
select c);
//CustomerID is a field in the Customer table
return customers;
}
}
I have then created a partial class, which retrieves the data from the DLL:
public partial class Customer
{
private string name;
public string Name
{
if (name==null)
{
DLLManager manager = new DLLManager();
name= manager.GetName(CustomerID);
}
return name;
}
}
In my business layer I can then call something like:
public class BLL
{
public List<Customer> GetCustomers()
{
DAL customersDAL = new DAL();
var customers = customersDAL.GetCustomers();
return customers.ToList();
}
}
...and this gives me a collection of Customers with ID and Name.
My problem is that I wish to page and sort by Customer Name, which as we have seen, is populated from a DLL. This means I cannot page and sort in the database, which is my preferred solution. I am therefore assuming I am going to have to call of the database records into memory, and perform paging and sorting at this level.
My question is - what is the best way to page and sort an in-memory collection. Can I do this with my List in the BLL above? I assume the List would then need to be stored in Session.
I am interested in people's thoughts on the best way to page and sort a field that does not come from the database in an Entity Framework scenario.
Very grateful for any help!
Mart
p.s. This question is a development of this post here:
GridView sorting and paging Entity Framework with calculated field
The only difference here is that I am now using a partial class, and hopefully this post is a little clearer.
Yes, you can page and sort within you list in the BLL. As long as its fast enough I wouldn't care to much about caching something in the session. An other way would be to extend your database with the data from you DLL.
I posted this question slightly differently on a different forum, and got the following solution.
Basically I return the data as an IQueryable from the DAL which has already been forced to execute using ToList(). This means that I am running my sorting and paging against an object which consists of data from the DB and DLL. This also allows Scott's dynamic sorting to take place.
The BLL then performs OrderBy(), Skip() and Take() on the returned IQueryable and then returns this as a List to my GridView.
It works fine, but I am slightly bemused that we are perfoming IQueryable to List to IQueryable to List again.
1) Get the results from the database as an IQueryable:
public class DAL
{
public IQueryable<Customer> GetCustomers()
{
Entities entities = new Entities();
var customers = (from c in entities.Customers
select c);
//CustomerID is a field in the Customer table
return customers.ToList().AsQueryable();
}
}
2) Pull the results into my business layer:
public class BLL
{
public List<Customer> GetCustomers(intint startRowIndex, int maximumRows, string sortParameter)
{
DAL customersDAL = new DAL();
return customersDAL.GetCustomers().OrderBy(sortParameter).Skip(startRowIndex).Take(maximumRows).ToList();
}
}
Here is the link to the other thread.
http://forums.asp.net/p/1976270/5655727.aspx?Paging+and+sorting+Entity+Framework+on+a+field+from+Partial+Class
Hope this helps others!
I created my model using Db Context Generator, using EF 4.
My model is like this:
Program Table:
ID
Name
Group Table:
ID
Name
ProgramID (Associated to Program.ID)
I want to display these columns in my grid:
Program.Name - Group.Name
But grdGroups.DataSource = db.Groups.ToList()
doesn't return Program.Name
When I try to this I get ObjectDisposedException.
Partial Public Class Group
Public ReadOnly Property ProgramName() As String
Get
Return Program.Name
End Get
End Property
End Class
What's the best way to return the Program.Name to include it in the grid datasource?
When I try to this I get
ObjectDisposedException
The problem is lazy loading - EF did not materialize the related Program entity, hence when you try to access Program.Name it will try and re-query the DB, but the context has been disposed at this point, so you get an exception.
You can use an Include() query when you retrieve your Group entity, to specify that you also want to load the related Program entity, i.e. :
var groups = context.Groups.Include(x => x.Program);
Suppose I have two table tab1, tab2. EF will create a edmx file and there are two entities created.
Then I want to add a computer member to tab1, which get some result from tab2, such as count, sum. What I used is partial class:
public partial class tab1{
public int Count{
get{
int cnt;
//...
return cnt;
}
}
public int Total{
get{
int total;
//the matching sql like select sum(column) from tab2
return total;
}
}
}
I want to cnt is counts in tab2(so the SQL should be select count(1) from tab2). Or total which is calculated from another table.
But how to implement it? there is no something like datacontext yet.
Yes there is - use the ObjectContext ! That's your "entry point into all things for Entity Framework.
You named it when you created the EDMX - it's the same name that's used for your Entity Framework connection string. It's a class in your "mymodel.designer.cs" code-behind file for the EDMX model.
using(MyModelContext ctx = new MyModelContext())
{
tab1 newTab = new tab1();
// set the properties as you wish
ctx.AddTotab1(newTab);
ctx.SaveChanges();
}
If your "tab1" and "tab2" entities are linked in a 1:n fashion (one "tab1" can have multiple "tab2" entries), you'll find a member of "tab1" of type "EntityCollection" - let's say this is called "tab2Entities".
Now if you want to calculate the number of "tab2" entries for a given "tab1" object, just use this code:
if(!tab2Entities.IsLoaded())
tab2Entities.Load();
int count = tab2Entities.Count;
That's all there is! :-)
Marc
If you're writing these sorts of properties yourself, it sounds like you haven't rigged up the entity framework navigation properties and association mappings.
Try add a foreign key to your database between the tab1 and tab2 tables (however they are related) and then wipe your edmx file and import the entire thing again. You should see that there is now an association between tab1 and tab2 in the entity framework designer.
You could then call something like:
myTab1.Tab2s.Count();
Hopefully that helps
- Loren Van Spronsen
I have an entity with self reference (generated by Entity Designer):
public MyEntity: EntityObject
{
// only relevant stuff here
public int Id { get...; set...; }
public MyEntity Parent { get...; set...; }
public EntityCollection<MyEntity> Children { get...; set...; }
...
}
I've written a stored procedure that returns a subtree of nodes (not just immediate children) from the table and returns a list of MyEntity objects. I'm using a stored proc to avoid lazy loading of an arbitrary deep tree. This way I get relevant subtree nodes back from the DB in a single call.
List<MyEntity> nodes = context.GetSubtree(rootId).ToList();
All fine. But when I check nodes[0].Children, its Count equals to 0. But if I debug and check context.MyEntities.Results view, Children enumerations get populated. Checking my result reveals children under my node[0].
How can I programaticaly force my entity context to do in-memory magic and put correct references on Parent and Children properties?
UPDATE 1
I've tried calling
context.Refresh(ClientWins, nodes);
after my GetSubtree() call which does set relations properly, but fetches same nodes again from the DB. It's still just a workaround. But better than getting the whole set with context.MyEntities().ToList().
UPDATE 2
I've reliably solved this by using EF Extensions project. Check my answer below.
You need to assign one end of the relationship. First, divide the collection:
var root = nodes.Where(n => n.Id == rootId).First();
var children = nodes.Where(n => n.Id != rootId);
Now, fix up the relationship.
In your case, you'd do either:
foreach (var c in children)
{
c.Parent = root;
}
...or:
foreach (var c in children)
{
root.Children.Add(c);
}
It doesn't matter which.
Note that this marks the entities as modfied. You'll need to change that if you intend to call SaveChanges on the context and don't want this saved.
The REAL solution
Based on this article (read text under The problem), navigation properties are obviously not populated/updated when one uses stored procedures to return data.
But there's a nice manual solution to this. Use EF Extensions project and write your own entity Materilizer<EntityType> where you can correctly set navigation properties like this:
...
ParentReference = {
EntityKey = new EntityKey(
"EntityContextName.ParentEntitySetname",
new[] {
new EntityKeyMember(
"ParentEntityIdPropertyName",
reader.Field<int>("FKNameFromSP")
)
})
}
...
And that's it. Calling stored procedure will return correct data, and entity object instances will be correctly related to eachother. I advise you check EF Extensions' samples, where you will find lots of nice things.
I'm having problems querying the entity model to get additional information.
My db has a Program table with a one to many relation with an Events table. The Entity model generates the relationships just fine, but I'm unable to figure out how to query the model to get the progam object with its events.
I can do this:
var foo = from program in entities.ProgramSet
where program.StartDate > DateTime.now
orderby program.StartDate
select program;
No problems there. From what I've found on Microsofts Page (Shaping queries with Entity framework): msdn.microsoft.com/en-us/library/bb896272.aspx, if I wanted to get the child objects, I just do the following:
// Define a LINQ query with a path that returns
// orders and items for a contact.
var contacts = (from contact in context.Contact
.Include("SalesOrderHeader.SalesOrderDetail")
select contact).FirstOrDefault();
However, there is no .Include or Include that I can find on the query.
Any suggestion? I know that I can do a foreach across the results, then run a .Events.Load() on it, but doesn't that force the IQueriable result to execute the sql, instead of optomize it to run only when a .ToList() etc is called on it?
Here is some sample code from my project:
public class ProgramRepository : CT.Models.IProgramRepository
{
CTEntities db = new CTEntities();
public IQueryable<Program> FindAllPrograms()
{
return db.ProgramSet;
}
public IQueryable<Program> FindUpcomingPrograms()
{
var programs = from program in FindAllPrograms()
where program.StartDate > DateTime.Now
orderby program.StartDate
select program;
return programs;
}
With the FindUpComingPrograms I would like to have it also include the Events Data. There is a relationship between the Program and Events model. Program has a List<Events> property, that I would like to fill and return with the IQueryable method.
Thanks again!
The Include Function is part of the ObjectQuery object...
I think you are going to need to re-write your query to look something like this:
var contacts = context.Contact.Include("SalesOrderHeader.SalesOrderDetail").FirstOrDefault();
//Not sure on your dot path you might have to debug that a bit
Here is an Article that has some examples...