Consider the model below. I have an Order class and an OrderLine class. The Order.TotalAmount is calculated through a view which performs an OUTER APPLY across all the Order.OrderLines.
[Table("SelectOrder")]
public class Order
{
public decimal TotalAmount { get; set; }
public virtual ICollection<OrderLine> OrderLines { get; set; }
}
[Table("SelectOrderLine")]
public class OrderLine
{
public decimal Amount { get; set; }
public virtual Order Order { get; set; }
}
I have decorated my classes with the TableAttribute to enable Entity Framework Core to get the data from the views to the entity. The TableAttribute actually points to the view instead.
Now I would like to perform inserts, updates and deletes. This poses a problem as it's not possible to use a view with an OUTER APPLY for these changes. I've tried using query types for this but you cannot define an entity as both a query type and an entity type. Doing so results in an error for me. So adding a TableAttribute with the actual table e.g. Order in combination with modelBuilder.Query<Order>().ToView("SelectOrder"); does not work.
I could create a separate class SelectOrder which is mapped to the view and map my Order entity to the table. Or I could build a custom attribute and perform some custom SQL generation by overriding the SqlServerQuerySqlGenerator.
But before I go down these roads... Is it really not possible to map an entity to both a view for selects and a table for inserts, updates and deletes?
Maybe not the answer you're looking for, but you could add a calculated OrderTotal attribute to the Order table in the database.
Since .NET 5 Preview version was released it's possible to support a separation of query and update the mapping
ref. https://github.com/dotnet/efcore/issues?q=is%3Aissue+milestone%3A5.0.0-preview2+is%3Aclosed+label%3Atype-enhancement+is%3Aclosed
Background Information
I am currently working with EF Core using a database first implementation.
Current tables
Fizz
{
[Id] INT
[Category] varchar
[Value] varchar
}
Buzz
{
[Id] UniqueIdentifier
[TypeId1] INT
[TypeId2] INT
CONSTRAINT [FK_Buzz_Fizz_1] FOREIGN KEY ([TypeId1] REFERENCES [Fizz][Id])
CONSTRAINT [FK_Buzz_Fizz_2] FOREIGN KEY ([TypeId2] REFERENCES [Fizz][Id])
}
Fizz currently acts a lookup table. Doing this allows for a single data repository to be used to find different values by category.
Buzz is a table that has two different type values to be stored e.g. TypeId1 could be brand which would exist in Fizz as (id, Brands, Nestle) and TypeId2 could be a flavor which would exist in Fizz as (id, Flavors, Grape).
The Issue
I scaffold the db to create the Data Models.
When running the application the following occurrs:
InvalidOperationException: Unable to determine the relationship represented by navigation property 'Buzz.TypeId1' of type 'Fizz'. Either manually configure the relationship, or ignore this property using the '[NotMapped]' attribute or by using 'EntityTypeBuilder.Ignore' in 'OnModelCreating'.
One solution that has occurred to me is to break this lookup table (Fizz) into multiple tables that way the references could be resolved by not having duplicate types used for Foreign Keys.
This would require re-work of the logic for the current data repository to either access multiple tables or be split into multiple data repos.
Another solution would be to modify the DBContext that is generated and use DataAnnotations on the DataModel. I would like to avoid doing this as the Context and Models will be regenerated in the future and these changes will be overwritten.
Is there a way to have a datamodel generated from a table that has multiple Foreign Keys to a single table without having to modify the generated code?
For posterity:
With the database approach a scaffold of the db is done to create the context and data models.
The data models generated (using the example tables above) look something like this -
public partial class Buzz
{
public Buzz()
{ }
public Guid Id { get; set; }
public int TypeId1 { get; set; }
public int TypeId2 { get; set; }
public Fizz TypeId1Fizz { get; set; }
public Fizz TypeId2Fizz { get; set; }
}
public partial class Fizz
{
public Fizz()
{ }
public int Id { get; set; }
public string Category { get; set; }
public string Value { get; set; }
public ICollection<Buzz> TypeId1Fizz { get; set; }
public ICollection<Buzz> TypeId2Fizz { get; set; }
}
The issue is that the relationship in Buzz could not be resolved.
The solution
When using scaffold on the database all models are generated as partials to a specified folder. I created a partial for the Buzz class in another directory that lives inside of the directory created by the scaffold (be sure that the namespaces match VS likes to add the directory name to the namespace and the partials won't be matched).
public partial class Buzz
{
[NotMapped]
public Fizz TypeId1Fizz { get; set; }
[NotMapped]
public Fizz TypeId2Fizz { get; set; }
}
but Leustherin then you lose the ability to utilize .Include for Fizz! EntityFramework won't create an SQL join statement for you so you will have to make an extra trip to the DB to obtain your look up value!
To get around this, override the Get or GetAll function of your data repository and create your own join statement.
Why I chose this solution
Maintainability.
Anytime the DataModels are regenerated instead of getting a runtime error there is now a compile error reminding the dev to delete the extra properties from the generated data model.
There is no other modification of automatically generated files.
There are no major schema changes done to accommodate the change.
I will do my best to keep this updated.
I have (can`t change) EF DataBase first project without navigation property in models.
I want extend autogenerated models and add navigation property
Generated model
//generated.cs
public partial class company
{
public int id { get; set; }
public string name { get; set; }
}
public partial class user
{
public int id { get; set; }
public int company_id { get; set; }
}
I want add navigation property from code
//model_extension.cs
public partial class user
{
public company Company { get; set; }
}
I have exception "The specified type member 'Company' is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties are supported."
I work with CodeFirst before.
I understand, I must link user.company_id to Company
But not understand how make this with code (not designer)
In Database First Approach, You are generating your POCO objects from database schema via Entity Framework Designer/ADO.NET Entity Data Model so it is not flexible as Code-First, you need to go on database, and change the schema yourself and update your .edmx file. while adding properties to these Models are possible in c# side, but they are not going to be added to your database schema,
I suggest your reverse your database schema and go as Code-First Approach, This nuget package can do this for you.
After Reversing It's all about Code-First then, creating your own DbContext and OnModelCreating and let the Migration handle the rest. Then you can use Eager Loading of EF to load your data,
I'm experimenting with EF5 Code First and I am using the models (show below).
When I look at the database that is created, I am confused because I do not see anything in the Track table that points to the Category table. Category has a FK pointing back to Track but that means that there are going to be duplicates of the categories?
A little background: I am trying to build a model that has tracks and every track can have 1 to N Categories. All of the categories are already defined, that is they are basically a lookup and I plan to create them in the seed method when database is created.
I think I am not understanding something obvious... When I query a track, how will I know what category it contains?
Thx
public class Track : IAuditInfo
{
public Int32 Id { get; set; }
public String Name { get; set; }
public String Description { get; set; }
public String Data { get; set; }
public DateTime CreatedOn { get; set; }
public DateTime ModifiedOn { get; set; }
public ICollection<Category> Categories { get; set; }
public Track()
{
Categories = new List<Category>();
}
}
public class Category
{
public Int32 Id { get; set; }
public Boolean IsVisible { get; set; }
public String DisplayName { get; set; }
}
Your current model is a one-to-many relationship between tracks and categories.
This usually implemented, as you have noted that entity framework does, using a foreign key on the many side (category) to the one side (track).
If I understand you correctly, what you want is a many-to-many relationship. Many tracks can be related to the same category, and a single track can belong to many categories.
To let entity framework understand that you want a many-to-many relationship you can simply add a ICollection property to your category class.
So both your classes should have a collection of the other class.
I.e. tracks have many categories and categories have many tracks.
For more information you can also see: http://msdn.microsoft.com/en-us/data/hh134698.a.nospx
Olav is right, your data model at the moment is not telling Entity Framework that there is a many-to-many relationship in there.
The simplest way to resolve this is to add
public virtual ICollection<Track> Tracks { get; set; }
to your Category class.
However... You may not want to pollute your domain model with artefacts that are not relevant to your domain. More importantly, when you do it this way, it is up to Entity Framework to figure out what to call the binding table. Prior to EF6 this naming is non deterministic (see http://entityframework.codeplex.com/workitem/1677), which may mean that two different machines compiling the same code will decide on different names for that table and cause some interesting migration problems in your production system.
The answer to both problems is to always explicitly manage many-to-many relationships with Fluent Configuration.
In your Data Context class, override the OnModelCreating, something like this:
public class MyDb : DbContext
{
public IDbSet<Track> Tracks { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<Track>()
.HasMany(t => t.Categories)
.WithMany()
.Map(c => c.ToTable("CategoriesForTracks"));
}
}
If you do this, you don't need to add a navigation property to your Category class, though you still can (if you do, you should use the overload for WithMany that allows you to specify a property).
Relationships between entities and how to map that to a relational database is inherently hard. For anything other than the simplest parent-child relationships you will want to use the fluent API to make sure you actually get what you want.
Morteza Manavi has a really good blog series describing relationships in EF Code First in exhaustive detail.
NOTE
You should usually make navigation properties virtual. So, you should change your Category class like this:
public virtual ICollection<Category> Categories { get; set; }
In theory, not making it virtual should just cause eager loading rather than lazy loading to happen. In practice I have always found lots of subtle bugs appearing when my navigation properties are not virtual.
I'm having problems setting up an Entity Framework 4 model.
A Contact object is exposed in the database as an updateable view. Also due to the history of the database, this Contact view has two different keys, one from a legacy system. So some other tables reference a contact with a 'ContactID' while other older tables reference it with a 'LegacyContactID'.
Since this is a view, there are no foreign keys in the database, and I'm trying to manually add associations in the designer. But the fluent associations don't seem to provide a way of specifying which field is referenced.
How do I build this model?
public class vwContact
{
public int KeyField { get; set; }
public string LegacyKeyField { get; set; }
}
public class SomeObject
{
public virtual vwContact Contact { get; set; }
public int ContactId { get; set; } //references vwContact.KeyField
}
public class LegacyObject
{
public virtual vwContact Contact { get; set; }
public string ContactId { get; set; } //references vwContact.LegacyKeyField
}
ModelCreatingFunction(modelBuilder)
{
// can't set both of these, right?
modelBuilder.Entity<vwContact>().HasKey(x => x.KeyField);
modelBuilder.Entity<vwContact>().HasKey(x => x.LegacyKeyField);
modelBuilder.Entity<LegacyObject>().HasRequired(x => x.Contact).???
//is there some way to say which key field this reference is referencing?
}
EDIT 2: "New things have come to light, man" - His Dudeness
After a but more experimentation and news, I found using a base class and child classes with different keys will not work by itself. With code first especially, base entities must define a key if they are not explicitly mapped to tables.
I left the suggested code below because I still recommend using the base class for your C# manageability, but I below the code I have updated my answer and provided other workaround options.
Unfortunately, the truth revealed is that you cannot accomplish what you seek without altering SQL due to limitations on EF 4.1+ code first.
Base Contact Class
public abstract class BaseContact
{
// Include all properties here except for the keys
// public string Name { get; set; }
}
Entity Classes
Set this up via the fluent API if you like, but for easy illustration I've used the data annotations
public class Contact : BaseContact
{
[Key]
public int KeyField { get; set; }
public string LegacyKeyField { get; set; }
}
public class LegacyContact : BaseContact
{
public int KeyField { get; set; }
[Key]
public string LegacyKeyField { get; set; }
}
Using the Entities
Classes that reference or manipulate the contact objects should reference the base class much like an interface:
public class SomeCustomObject
{
public BaseContact Contact { get; set; }
}
If later you need to programmatically determine what type you are working with use typeof() and manipulate the entity accordingly.
var co = new SomeCustomObject(); // assume its loaded with data
if(co.Contact == typeof(LegacyContact)
// manipulate accordingly.
New Options & Workarounds
As I suggested in comment before, you won't be able to map them to a single view/table anyway so you have a couple options:
a. map your objects to their underlying tables and alter your "get/read" methods on repositories and service classes pull from the joined view -or-
b. create a second view and map each object to their appropriate view.
c. map one entity to its underlying table and one to the view.
Summary
Try (B) first, creating a separate view because it requires the least amount of change to both code and DB schema (you aren't fiddling with underlying tables, or affecting stored procedures). It also ensures your EF C# POCOs will function equivalently (one to a view and one to table may cause quirks). Miguel's answer below seems to be roughly the same suggestion so I would start here if it's possible.
Option (C) seems worst because your POCO entities may behave have unforseen quirks when mapped to different SQL pieces (tables vs. views) causing coding issues down the road.
Option (A), while it fits EF's intention best (entities mapped to tables), it means to get your joined view you must alter your C# services/repositories to work with the EF entities for Add, Update, Delete operations, but tell the Pull/Read-like methods to grab data from the joint views. This is probably your best choice, but involves more work than (B) and may also affect Schema in the long run. More complexity equals more risk.
Edit I'm not sure this is actually possible, and this is why:
The assumption is that a foreign key references a primary key. What you've got is two fields which are both acting as primary keys of vwContact, but depending on which object you ask it's a different field that's the primary key. You can only have one primary key at once, and although you can have a compound primary key you can't do primary key things with only half of it - you have to have a compound foreign key with which to reference it.
This is why Entity Framework doesn't have a way to specify the mapping column on the target side, because it has to use the primary key.
Now, you can layer some more objects on top of the EF entities to do some manual lookup and simulate the navigation properties, but I don't think you can actually get EF to do what you want because SQL itself won't do what you want - the rule is one primary key per table, and it's not negotiable.
From what you said about your database structure, it may be possible for you to write a migration script which can give the contact entities a consistent primary key and update everything else to refer to them with that single primary key rather than the two systems resulting from the legacy data, as you can of course do joins on any fields you like. I don't think you're going to get a seamlessly functional EF model without changing your database though.
Original Answer That Won't Work
So, vwContact contains a key KeyField which is referenced by many SomeObjects and another key LegacyKeyField which is referenced by many LegacyObjects.
I think this is how you have to approach this:
Give vwContact navigation properties for SomeObject and LegacyObject collections:
public virtual ICollection<SomeObject> SomeObjects { get; set; }
public virtual ICollection<LegacyObject> LegacyObjects { get; set; }
Give those navigation properties foreign keys to use:
modelBuilder.Entity<vwContact>()
.HasMany(c => c.SomeObjects)
.WithRequired(s => s.Contact)
.HasForeignKey(c => c.KeyField);
modelBuilder.Entity<vwContact>()
.HasMany(c => c.LegacyObjects)
.WithRequired(l => l.Contact)
.HasForeignKey(c => c.LegacyKeyField);
The trouble is I would guess you've already tried this and it didn't work, in which case I can't offer you much else as I've not done a huge amount of this kind of thing (our database is much closer to the kinds of thing EF expects so we've had to do relatively minimal mapping overrides, usually with many-to-many relationships).
As for your two calls to HasKey on vwContact, they can't both be the definitive key for the object, so it's either a compound key which features both of them, or pick one, or there's another field you haven't mentioned which is the real primary key. From here it's not really possible to say what the right option there is.
You should be able to do this with two different objects to represent the Contact view.
public class vwContact
{
public int KeyField { get; set; }
public string LegacyKeyField { get; set; }
}
public class vwLegacyContact
{
public int KeyField { get; set; }
public string LegacyKeyField { get; set; }
}
public class SomeObject
{
public virtual vwContact Contact { get; set; }
public int ContactId { get; set; } //references vwContact.KeyField
}
public class LegacyObject
{
public virtual vwLegacyContact Contact { get; set; }
public string ContactId { get; set; } //references vwLegacyContact.LegacyKeyField
}
ModelCreatingFunction(modelBuilder)
{
// can't set both of these, right?
modelBuilder.Entity<vwContact>().HasKey(x => x.KeyField);
modelBuilder.Entity<vwLegacyContact>().HasKey(x => x.LegacyKeyField);
// The rest of your configuration
}
I have tried everything that you can imagine, and found that most solutions won't work in this version of EF... maybe in future versions it supports referencing another entity by using an unique field, but this is not the case now. I also found two solutions that work, but they are more of a workaround than solutions.
I tried all of the following things, that didn't work:
Mapping two entities to the same table: this is not allowed in EF4.
Inheriting from a base that has no key definitions: all root classes must have keys, so that inherited classes share this common key... that is how inheritance works in EF4.
Inheriting from base class that defines all fields, including keys, and then use modelBuilder to tell wich base-properties are keys of the derived types: this doesn't work, because the methos HasKey, Property and others that take members as parameters, must reference members of the class itself... referencing properties of a base class is not allowed. This cannot be done: modelBuilder.HasKey<MyClass>(x => x.BaseKeyField)
The two things that I did that worked:
Without DB changes: Map to the table that is source of the view in question... that is, if vwContact is a view to Contacts table, then you can map a class to Contacts, and use it by setting the key to the KeyField, and another class mapping to the vwContacts view, with the key being LegacyKeyField. In the class Contacts, the LegacyKeyField must exist, and you will have to manage this manually, when using the Contacts class. Also, when using the class vwContacts you will have to manually manage the KeyField, unless it is an autoincrement field in the DB, in this case, you must remove the property from vwContacts class.
Changing DB: Create another view, just like the vwContacts, say vwContactsLegacy, and map it to a class in wich the key is the LegacyKeyField, and map vwContacts to the original view, using KeyField as the key. All limitations from the first case also applies: the vwContacts must have the LegacyKeyField, managed manually. And the vwContactsLegacy, must have the KetField if it is not autoincrement idenitity, otherwise it must not be defined.
There are some limitations:
As I said, these solutions are work-arounds... not real solutions, there are some serious implications, that may even make them undesirable:
EF does not know that you are mapping two classes to the same thing. So when you update one thing, the other one could be changed or not, it depends if the objects is cached or not. Also, you could have two objects at the same time, that represents the same thing on the backing storage, so say you load a vwContact and also a vwContactLegacy, changes both, and then try to save both... you will have to care about this yourself.
You will have to manage one of the keys manually. If you are using vwContacts class, the KeyFieldLegacy is there, and you must fill it. If you want to create a vwContacts, and associate is with a LegacyObject, then you need to create the reference manually, because LegacyObject takes a vwContactsLegacy, not a vwContacts... you will have to create the reference by setting the ContactId field.
I hope that this is more of a help than a disillusion, EF is a powerfull toy, but it is far from perfect... though I think it's going to get much better in the next versions.
I think this may be possible using extension methods, although not directly through EF as #Matthew Walton mentioned in his edit above.
However, with extension methods, you can specify what to do behind the scenes, and have a simple call to it.
public class LegacyObject
{
public virtual vwContact Contact { get; set; }
public string ContactId { get; set; } //references vwContact.LegacyKeyField
}
public class LegacyObjectExtensions
{
public static vwContact Contacts(this LegacyObject legacyObject)
{
var dbContext = new LegacyDbContext();
var contacts = from o in legacyObject
join c in dbContext.vwContact
on o.ContactId == c.LegacyKeyField
select c;
return contacts;
}
}
and
public class SomeObject
{
public virtual vwContact Contact { get; set; }
public int ContactId { get; set; } //references vwContact.KeyField
}
public class SomeObjectExtensions
{
public static vwContact Contacts(this SomeObject someObject)
{
var dbContext = new LegacyDbContext();
var contacts = from o in someObject
join c in dbContext.vwContact
on o.ContactId == c.KeyField
select c;
return contacts;
}
}
Then to use you can simply do like this:
var legacyContacts = legacyObject.Contacts();
var someContacts = someObject.Contacts();
Sometimes it makes more sense to map it from the other end of the relationship, in your case:
modelBuilder.Entity<LegacyObject>().HasRequired(x => x.Contact).WithMany().HasForeignKey(u => u.LegacyKeyField);
however this will require that u.LegacyKeyField is marked as a primary key.
And then I'll give my two cents:
if the Legacy db is using LegacyKeyField, then perhaps the legacy db will be read only. In this case we can create two separate contexts Legacy and Non-legacy and map them accordingly. This can potentially become a bit messy as you'd have to remember which object comes from which context. But then again, nothing stops you from adding the same EF code first object into 2 different contexts
Another solution is to use views with ContactId added for all other legacy tables and map them into one context. This will tax performance for the sake of having cleaner context objects, but this can be counteracted on sql side: indexed views, materialized views, stored procs, etc. So than LEGACY_OBJECT becomes VW_LEGACY OBJECT with CONTACT.ContactId brought over, then:
modelBuilder.Entity<LegacyObject>().ToTable("VW_LEGACY_OBJECT");
modelBuilder.Entity<LegacyObject>().HasRequired(x => x.Contact).WithMany().HasForeignKey(u => u.ContactId);
I personally would go with creating "mapper views" with CustomerId on legacy tables, as it's cleaner from c# layer perspective and you can make those views look like real tables. It is also difficult to suggest a solution without knowing what exactly is the scenario that you have a problem with: querying, loading, saving, etc.