4.2 Referential constraint

The following sample codes can be used for Web API OData V3 & V4 with a little bit function name changing.

Define Referential Constraint Using Attribute

There is an attribute named “ForeignKeyAttribute” which can be place on:

1.the foreign key property and specify the associated navigation property name, for example:

public class Order
{
    public int OrderId { get; set; }

    [ForeignKey("Customer")]
    public int MyCustomerId { get; set; }

    public Customer Customer { get; set; }
}

2.a navigation property and specify the associated foreign key name, for example:

public class Order
{
    public int OrderId { get; set; }

    public int CustId1 { get; set; }
    public string CustId2 { get; set; }

    [ForeignKey("CustId1,CustId2")]
    public Customer Customer { get; set; }
}

Where, Customer has two keys.

Now, you can build the Edm Model by convention model builder as:

public IEdmModel GetEdmModel()
{            
    ODataConventionModelBuilder builder = new ODataConventionModelBuilder();
    builder.EntitySet<Customer>("Customers");
    builder.EntitySet<Order>("Orders");
    return builder.GetEdmModel();
}

Define Referential Constraint Using Convention

If user doesn’t add any referential constraint, Web API will try to help user to discovery the foreign key automatically. There are two conventions as follows: 1.With same property type and same type name plus key name. For example:

public class Customer
{ 
   [Key]
   public string Id {get;set;}
   public IList<Order> Orders {get;set;}
}
public class Order
{
    public int OrderId { get; set; }
    public string CustomerId {get;set;}
    public Customer Customer { get; set; }
}

Where, Customer type name “Customer” plus key name “Id” equals the property “CustomerId” in the Order.

2.With same property type and same property name. For example:

public class Customer
{ 
   [Key]
   public string CustomerId {get;set;}
   public IList<Order> Orders {get;set;}
}

public class Order
{
    public int OrderId { get; set; }
    public string CustomerId {get;set;}
    public Customer Customer { get; set; }
}

Where, Property (key) “CustomerId” in the Customer equals the property “CustomerId” in the Order.

Now, you can build the Edm Model using convention model builder same as above section.

Define Referential Constraint Programmatically

You can call the new added Public APIs (HasRequired, HasOptional) to define the referential constraint when defining a navigation property. For example:

public class Customer
{
    public int Id { get; set; }
       
    public IList<Order> Orders { get; set; }
}

public class Order
{
    public int OrderId { get; set; }
 
    public int CustomerId { get; set; }         

    public Customer Customer { get; set; }
}

ODataModelBuilder builder = new ODataModelBuilder();
builder.EntityType<Customer>().HasKey(c => c.Id).HasMany(c => c.Orders);
builder.EntityType<Order>().HasKey(c => c.OrderId)
    .HasRequired(o => o.Customer, (o, c) => o.CustomerId == c.Id);
    .CascadeOnDelete();

It also supports to define multiple referential constraints, for example:

builder.EntityType<Order>()
    .HasKey(o => o.OrderId)
    .HasRequired(o => o.Customer, (o,c) => o.Key1 == c.Id1 && o.Key2 == c.Id2);

Define Nullable Referential Constraint Using Convention

Currently, it doesn’t suppport to define nullable referential constraint from attribute and convention method. However, you can do it by Programmatically by calling HasOptional() method:

For example:

public class Product
{
    [Key]
    public int ProductId { get; set; }

    public int SupplierId { get; set; }

    public Supplier Supplier { get; set; }
}

public class Category
{
    [Key]
    public int CategoryId { get; set; }
}

ODataModelBuilder builder = new ODataModelBuilder();
builder.EntitySet<Product>("Product");
var product = builder.EntityType<Product>().HasOptional(p => p.Supplier, (p, s) => p.SupplierId == s.SupplierId);

Then you can get the following result:

<EntityType Name="Product">
    <Key>
      <PropertyRef Name="ProductId" />
    </Key>
    <Property Name="SupplierId" Type="Edm.Int32" />
    <Property Name="ProductId" Type="Edm.Int32" Nullable="false" />
    <Property Name="CategoryId" Type="Edm.Int32" />
    <NavigationProperty Name="Supplier" Type="WebApiService.Supplier">
      <ReferentialConstraint Property="SupplierId" ReferencedProperty="SupplierId" />
    </NavigationProperty>
    <NavigationProperty Name="Category" Type="WebApiService.Category" />
</EntityType>

Where, CategoryId is nullable while navigation property Supplier is nullable too.

Thanks.