i am new to Entity Data framework
i have tables
Actions ( Actionid (pk) ,Actionname , ... )
Roles ( Roleid(pk) , Rolename , .... )
ActionRoles( Actionid(pk,fk) , Roleid(fk) ) [Mapping Table]
Please Suggest me the LINQ to get the RoleNames for Perticular ActionID
(Note : there is No class created with Name ActionRoles in entitydesigner.cs as because it doesn't have any other column name then ActionId and RoleID )
Thank you in Advance
When you have a link table like this, adding all tables to the Entity Model should create 2 way relationship Properties between the 2 end tables, hiding the link table completely allowing you to access via something like:
IEnumerable<string> roleNames = Entities.Actions
.First(a => a.Actionid == actionid)
.Roles
.Select(r => r.Rolename);
where actionid is an int variable containing the actionid you're interested in.
For a discussion of how to handle many-to-many relationships such as this (both foreign keys must be in the ActionRoles primary key as indicated in the comment to your question), see these tutorials:
For EF 4.0: http://www.asp.net/entity-framework/tutorials/the-entity-framework-and-aspnet-–-getting-started-part-5
For Ef 4.1: http://www.asp.net/entity-framework/tutorials/updating-related-data-with-the-entity-framework-in-an-asp-net-mvc-application
Related
I have the following Schema:
User Table: (Primary Key)
UserId
CustomerId
Role Table: (Primary Key)
UserId
CustomerId
UserRole Table:
UserRoleId (UNIQUEIDENTIFIER (newsequentialid)) Primary Key
UserId
Customerid
RoleId
Those tables participate in many to many relationship (UserRole). I am using Entity Framework code first with mapping classes to define the database tables. So, In my mapping class for User Table, I have the following:
this.HasMany(u => u.Roles)
.WithMany()
.Map(m =>
{
m.MapLeftKey(new string[] { "CustomerID", "UserID" });
m.MapRightKey(new string[] {"CustomerID", "RoleID"});
m.ToTable("UserRoles");
}
);
Entity framework is failing with this message:
"One or more validation errors were detected during model generation:
CustomerID: Name: Each property name in a type must be unique. Property name 'CustomerID' is already defined.
UserRole: EntityType: EntitySet 'UserRole' is based on type 'UserRole' that has no keys defined.
is it possible to tell Code First that the Primary Key for my "UserRole" is UserRoleId?
The issue is when Entity Framework tries to create the UserRole Table, it would use all columns of MapLeftKey and MapRightKey to Create UserRole with PrimaryKey that has all those columns.
Any suggestions?
You need to model your classes similar to your DB, why don't you simply add the association tables? I mocked up your DB and there is no problem as long as you model all the tables.
Test it for yourself, create an EF project .edmx using code first from existing DB, I think the answer will be obvious.
If you have database tables with relationships as follows:
Person
PersonId (PK), Name
PersonDoesService
PersonId (FK), ServiceId (FK)
Service
ServiceId (PK), Type
Is it possible with Entity Framework in one statement to get all Persons that does one service based on serviceId?
The code below will do what you are asking. Make sure that your ServiceId exists.
var people = context.Service.First(s => s.ServiceId == theServiceIdIWant).Person // IEnumerable<Person>
I got products table
->productID - primary
->price
->Quantity
productCategory -table
->prodcatID- primary
->prodId - foreign key
->catID - foreign key
productlanguages - table
->prodID - foreign key
->langID - forein key
->Title
So I use Entity framework and I shoud somehow get all products WITH THEIR TITLE,QUANTITYI PRICE From GIVEN CATEGORY AND FROM GIVEN LANGUAGE.
SO i should somehow combine info from all these three table
so i made my first function to get all products from given category
public List<ProductCategories> GetAllProductsForCategory(int catID)
{
using (OnlineStoreDBContext db = new OnlineStoreDBContext())
{
List<ProductCategories> lst = db.ProuctCategories.Where(x => (x.CategoryID == catID)).ToList();
}
}
So now I have a list with all productID that match this category. But now how to get the data from the other two.
See Loading Related Entities: http://msdn.microsoft.com/en-au/data/jj574232.aspx
My code:
Models.Resource r = new Models.Resource();
r.Name = txtName.Text;
r.ResourceType = resTypes.Find(rt => rt.Name == "Content");
r.ResourceContents.Add(_resourceContent.Find(rc => rc.ID == _resourceContentID));
ctx.Resource.Add(r);
ctx.SaveChanges();
ctx.SaveChanges() causes the error:
Cannot insert explicit value for identity column in table 'Resources' when IDENTITY_INSERT is set to OFF.
Looking at what's being sent to SQL:
ADO.NET:Execute NonQuery "INSERT [dbo].[Resources]([ID], [Name], [Description], [IsOnFile],
[ContentOwnerAlias], [ContentOwnerGroup], [ResourceTypes_ID])
VALUES (#0, #1, #2, #3, #4, #5, NULL)"
My POCO Resource has ID as a Key:
public partial class Resource
{
public Resource()
{
}
[Key]
public int ID { get; set; }
And my Map code:
public class ResourceMap : EntityTypeConfiguration<Resource>
{
public ResourceMap()
{
// Primary Key
this.HasKey(t => t.ID);
How do I tell Entity to not send the Key ID field to the database?
If your PK is generated by the database (like an identity) you have to configure it in your Map.
public class ResourceMap : EntityTypeConfiguration<Resource>
{
public ResourceMap()
{
// Primary Key
this.HasKey(t => t.ID);
this.Property(t => t.ID).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
}
}
You do not need the HasKey(t => t.ID) Fluent API mapping or the [Key] Data Attribute because by convention EF will assume that an integer field named ID is the key and is database generated.
As an aside, I'd recommend that when you are not following conventions you should choose one method or the other - otherwise you are repeating yourself and when you want to change something you need to change it in 2 places.
I'm not sure why the field in the database isn't already database generated - maybe when you define the field via the fluent api you have to specify that too. What I do know is that in order to make EF change a key field to be database generated you will need to drop the table.
So - rollback the migration or drop the table / database, then remove the data attribute, remove the fluent mapping and recreate.
This issue is currently on a "backlog" in the entity framework. If you want to vote for it you can do that here: Migrations: does not detect changes to DatabaseGeneratedOption
Other References:
Identity problem in EF
Switching Identity On/Off With A Custom Migration Operation
I have an Entity. Mandate. Every mandate has a required:many relation to a Person (NavigationProperty). I use the DbContext API with (LazyLoadingEnabled, AutoDetectChangesEnabled, ValidateOnSaveEnabled, ProxyCreationEnabled)
Now I like to delete a Mandate entity. The mandate entities are loaded by another context with AsNoTracking().
message.Result.
ObserveOn(On<DataComposition>.Scheduler).
Where(r => r).
Subscribe(_ =>
{
using (var unit = UnitOfWork.Begin())
{
var mandate = this.SelectedItem.OriginalEntity;
this.mandateRepository.Attach(mandate);
// mandate.Person.ToString();
this.mandateRepository.Delete(mandate);
unit.Commit();
}
this.List.RemoveOnUi(this.SelectedItem);
});
Now during committing I get the following exception: Entities in 'CodeFirstContainer.Mandates' participate in the 'Mandate_Person' relationship. 0 related 'Mandate_Person_Target' were found. 1 'Mandate_Person_Target' is expected.
The delete works if I include the Person Property during the population/selection or if I visit the Property (lazyloading), but I DONT LIKE to materialize/hold many entities only for the deletion case and I DONT LIKE to trigger more than a single DELETE query to db!
The fact that, if you have the navigation property mandate.Person populated, the following SQL statement ...
delete [dbo].[Mandates]
where (([Id] = #0) and ([PersonId] = #1))
... is sent to the database, lets me think that the navigation property indeed must be populated with a person with the correct PersonId to delete the parent.
I have no idea why Entity Framework just doesn't send a delete statement with the primary key ...
delete [dbo].[Mandates]
where ([Id] = #0)
... as I had expected.
Edit
If the Mandate entity has a foreign key property PersonId for the Person navigation property, the expected SQL (the second above) is sent to the database. In this case the Person navigation property can be null and the value of the FK property PersonId doesn't matter.
Edit 2
If you don't want to introduce a FK property the way with the least DB-roundtrip-costs would probably be to fetch the person's Id and then create a dummy person with that key in memory:
// ...
var personId = context.Mandates
.Where(m => m.Id == mandate.Id)
.Select(m => m.Person.Id)
.Single();
mandate.Person = new Person { Id = personId };
this.mandateRepository.Attach(mandate);
this.mandateRepository.Delete(mandate);
// ...