I am working on a simple database and to be specific here is the model generated by database first approach (Visual Studio 2017 Community, Entity Framework 6.2):
Generated Database Model
I'd like the UserMessage table to be able to point to itself with a field named AnswerId, this is a nullable foreign key referencing its primary key. Again, to be specific, here is the part where I create the table:
UserMessage table script
My problem is that when Entity Framework generates the classes based on the existing database everything goes fine except for this particular table, in which EF suggests (I don't know why) that the UserMessage table has a multiplicity of 0..1 - * to itself while it should 1 - 0..1 (because a message may have a direct answer, but not more than 1, though that message, which is the answer, could also have an answer, so it's just like a linked list).
Here is the generated class: UserMessage generated class
To sum up the whole thing: I'd like to know why Entity Framework generates my class the way it does, and how could I make it generate it so that I only have a virtual property pointing to the answer (in case it has one), but not a collection.
Thank you for your answers!
I think what you're seeing is a correct interpretation by EntityFramework.
UserMessage1 represents a collection of all the UserMessages that have references to the parent as their answer. I understand that you probably won't use that collection for anything but it's not wrong that it's there. UserMessage2 seems to be the property you're looking for. Maybe you could rename those properties in the diagram so they're not confusing.
UserMessages1 = MessagesThatReferenceMe
UserMessages2 = the Message that I may or may not reference
I don't see how you can stop EF from generating this collection. I think if you delete the property in the diagram you will have to delete it every time you update the diagram.
Maybe try deleting the 2nd UserMessage navigation property in your model.
Related
I choose Database First:
Here is an example table that is experiencing this issue. As you can see the EntityId column is the Primary Key:
The imported table in the model browser shows that it has the Primary Key:
But the code for the generated class does not have the EntityId column decorated with a Key attribute:
At run time I get this error:
Additional information: One or more validation errors were detected
during model generation: EntityType 'Entity' has no key defined.
Define the key for this EntityType.
Why do I have to manually decorate the EntityId column with the Key Attribtue? Shouldnt EntityFramework take care of all that considering it is Database first?
Typically speaking I have experience with EF4 through EF 6.1.3 and a teeny bit with Entity Core (was EF7 and then MS fun with naming). Typically if you are doing database first you do not get an adornment from your t4 template. I just looked at mine just now and I have no adornment for the key, just for constructor and the reference to the navigation of teOrder back to it.
I can save an Entity just fine and my code runs with this:
using (var context = new EntityTesting.TesterEntities())
{
var nPerson = new tePerson { FirstName = "Test", LastName = "Tester" };
context.tePerson.Add(nPerson);
context.SaveChanges();
}
What I would suggest is:
Go to your (name).edmx Entity File and on the design surface wipe out the object and then replace it on the surface. In countless times this has fixed issues with the generated objects. When you SAVE it should auto run the T4 templates (*.tt files). If not you can select them, right click and select 'Run Custom Tool'. This just generates the POCO objects or the Context objects.
If this is really a fault with the table it is typically with it NOT having a key. You are showing it does though. Is there anyway to mirror the exact same table logic and confirm the key has nothing out of the ordinary and is just a plain old key Primary Key?
Create a brand new table with similar structure but not an exact copy and a new Entity File and confirm you can create it.
Tables are pretty straight forward with EF, or as straight forward as EF can be. You create them in SQL, ensure you have a key, add it to a design surface, save, it generates the objects for you. If you have other things under the hood like custom procs hooked to it or other out of the ordinary nav items that would be one thing. The only other thing would be if it has a very old SQL Type as the key. I know that the 'Text' type and EF do not play nice together. There may be other types that behave the same way.
This issue was fixed by including the "metadata" part of the connection string.
At first my connection string looked like this:
data source=.;initial catalog=TestDatabase;integrated security=True;MultipleActiveResultSets=True;App=EntityFramework;
Which produced the error.
Changing my connection string to this:
metadata=res://*/DbContexts.TestContext.csdl|res://*/DbContexts.TestContext.ssdl|res://*/DbContexts.TestContext.msl;provider=System.Data.SqlClient;provider connection string="data source=.;initial catalog=TestDatabase;integrated security=True;MultipleActiveResultSets=True;App=EntityFramework"
Allowed operations on the Context to be performed with no error encountered
I'm using Entity Framework 6, with POCO and fluent-API and I've noticed an annoying bug.
If I have an entity called MyEntity and this entity has a property called MyProp, that makes it impossible to create an entity called MyEntity_MyProp.
Exception:
The item with identity 'MyEntity_MyProp' already exists in the metadata collection.\r\nParameter name: item
The error immediately goes away if I rename any of the entities, or rename the properties.
The "bug" is obvious: the key [EntityName]_[PropertyName] must be unique in the metadata collection.
Screenshot:
I'm migrating a huge Entity Framework model with 390+ classes from EF 4, database first, to EF 6, code first, with fluent-API. It's out of question to rename the entities or the tables.
How do I solve that?
EDIT
This SO question doesn't have anything to do with my problem: The item with identity 'Id' already exists in the metadata collection. Parameter name: item
This bug happens when you use underscores in the name of your entities. The reason is Entity Framework also uses underscores to create the names of the keys (concatenating the entity and property names).
So, if you have an entity named "Table" with a property "Prop" and a table named "Table_Prop" a clash will occur. This is most likely what happened.
It's a known bug. It's currently scheduled to be fixed in an arbitrary future version, that is, it's not in the road-map yet.
Source: https://entityframework.codeplex.com/workitem/2084
EDIT:
According to #Anthony, this was fixed in v6.1.3
I was able to work around this by adding the Table attribute on the EF table object, and then renaming the object to something like MyEntityMyProp. I then refactored by code to use the new object name. This was more simple than renaming the database table.
[Table("MyEntity_MyProp")]
public class MyEntityMyProp
{
...
}
Please check ApplicationDbContext in your project.
maybe your entity name used as the property name in public DbSet<>.
I'm using generated POCO classes and Entity Framework.
In order to make the code less complex I'm trying to remove all navigation properties from the code while still keeping the Foreign Key constraints in the database (navigation properties do more harm than good for us).
If I remove them manually from the POCO-classes I get the following error
The entity type UserEntity is not part of the model for the current context
If I try to remove them from the .edmx-file I get the following error:
Error 3 Error 3015: Problem in mapping fragments starting at lines 479, 562:Foreign key constraint 'fk_StorageContracts_User1' from table StorageContract (OwnerUserID) to table User (ID):: Insufficient mapping: Foreign key must be mapped to some AssociationSet or EntitySets participating in a foreign key association on the conceptual side.
Is there any way to remove navigation properties from POCO-classes without removing the corresponding FK?
I know this is old, but, since there is still no answer, I thought I'd give it a try:
I am still working in EF 4.0, but, following the example to which you referred, you have an xxxModel.tt. If you are willing to tweak that, you can find where it generates the Navigation Properties and change them to be simple auto-properties. I had a similar project where I generated them like this:
public List<NavDataX> NavDataXs
{
get; set;
}
Now, they are still there, but they are null until you explicitly set them. Doing it this way, I did not mess with the EDMX and did not encounter the two errors you mentioned.
I have these two related tables Client (ClientId, Name) and ClientDescription (ClientDescriptionId, (FK) ClientId, Description). That is to say each Client can have many associated descriptions. Now, when displaying the a list of ClientDescriptions, I also need to know what the Name of it's associated Client is.
Now you'll probably say that I allready have this information, since I can simply follow my navigation property back to the associated Client and use its Name. I can't do that because I'm autogenerating a grid in Ria services, and this just gives me a count for navigation properties, and I haven't found a way to flatten this down in my metadata file. Hence why I want a property.
The whole idea is that I want to be able to add a new field to my database, update my entity classes from the database and regenerate my domain service, and the new field should just pop up in my grid. I shouldn't have to update my xaml just because my database happen to have an extra field.
So, what I would like to do is add a ClientName field to the entity (clr object), but keep my database clean (no such denormalization in the db).
So, I generated my edmx, and added a new property named ClientName. Set it to StoreGeneratedPattern.Computed, and compiled. I then get a nasty little error
Error 3004: Problem in mapping fragments starting at line NN: No mapping specified for properties (etc..)
The solution apparently is to generate my database from my edmx. (Or that's what answers to questions about that error seems to yield.) But this generates an actual DB-field, which I don't want, so that answer doesn't apply to my case.
So my question is: How can I denormalize my clr entity, but keep my db tables normalized?
Edit: I guess this question can be generalized a bit. The issue would be the same if ClientDescription contained a few numeric fields that I wanted to do some calculations on, and I wanted the result available as a field and the algorithm should be in c# rather than in my database.
To answer your more generalized question:
Entities are generated by the Entity Framework with a partial keyword.
This means that the code of an entity can be split in multiple source files in the same namespace and assembly. One will contain the generated code from the Entity Framework, the other will contain custom properties and methods.
If for example, your entity has the database fields Price and Amount you could add a property in the partial class TotalPrice which would return Price * Amount.
Then the algorithm will be C# and your database won't know about the extra property.
Ive got a WPF app, following the Model View ViewModel pattern, using the Entity Framework to interact with a SQL 2008 database.
Problem:
My problem is i can't change a foreign key value in the databse using EF. I have two entities: Site and Key. A Site can have many Keys on it. I would like to move a Key from one Site to another. I'm trying to do this using the following code:
keyToMove.Site = newSite;
dataAccess.SaveChanges(); // this method just does: this.entities.SaveChanges();
What I've Observed
It appears in memory everything is fine as the rest of the app reflects this change (the Key will appear under the new Site). However, the foreign key in the database does not change, and upon closing and restarting the app, all changes are lost.
After "keyToMove.Site = newSite;", keyToMove, newSite and the old Site instance all have an EntityState value of "Unchanged" which can't be right. Also SaveChanges is returning 2, which is just confusing me even further.
The setter implementation for the "Site" property looks like other navigation properties in my model:
set
{
((global::System.Data.Objects.DataClasses.IEntityWithRelationships)(this)).RelationshipManager.GetRelatedReference<Site>("CmsModel.SiteKeyAssociation", "Site").Value = value;
}
SQL Profiler shows that nothing resembling an UPDATE is sent to the db engine, only a very, very long SELECT.
Things which may have an effect
The "Key" entity inherits from another entity based on a condition applied to one of the columns.
I'm using the AutoFac IOC container to supply any ViewModels who want to do some data access with a reference to an instance of my data access class ("dataAccess" in the example).
An ObjectContext instance is a member of this class (shown in comments as "this.entities").
The dataAccess instance is Singleton Scoped so there should only be one instance being shared among the View Models e.i. both "keyToMove" and "newSite" are attached to the same context.
Sorry for the length of this post, but i seriously have no idea whats going on here and ive tried to provide as many details which may help as possible. Please ask if any further info would help.
Thanks in advance.
I'm in the process of teaching myself the entity framework myself, so I may be missing the point of your question, and am certainly no expert. However, that being said, you may be running into a problem I had to work through myself.
You didn't post the code where you are creating your "newSite" variable, but when setting foreign keys in EF you do it differently than you would in Linq or just working in the database. With EF, you have to select IN your foreign key value that you want to set on your object and then set it.
This will not work:
NewSite = Site.CreateSite("PrimaryKeyValue");
keyToMove.Site = NewSite;
Instead, you do something like this:
NewSite = MyEntities.Site.Where(site=>site.PrimaryKey==PrimaryKeyValue)
.FirstOrDefault();
keyToMove.Site = NewSite;
I hope I understood your question!
Regards,
Mike