OData $ expand不包括扩展属性为null的实体

Question

I have an OData service build with WebAPI and EF 6. I use the fluent api to create my models. It works fine, but when I use $expand it omits entities where the expanded property is null .

This is a simplified example:

public class Customer
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int? AddressId { get set; } // Note that Address is optional
    public Address Address { get; set; }
}

public class Address
{
    public int Id { get; set; }
    public string Street{ get; set; }
}


public class CustomersController : ODataController
{
    [EnableQuery]
    public virtual IQueryable<Customer> Get(ODataQueryOptions<Customer> q)
    {
        // I return IQueryable from DBSet here...
        return db.GetDbSet<Customer>();
    }
}

A Customer doesn't need to have an address. And If I query it like /customers?$expand=Address it will not include Customers where Address == null . It will only return the Customer entities where Customer.Address exists.

I guess it does an inner join, and therefore doesn't get the Customer entities that doesn't have an Address . Is there any way to include customers where address is null as well?

Current Output:

[
    {
        Id: 1,
        Name: 'Customer1',
        AddressId: 1,
        Address : 
        {
            Id: 1,
            Street: 'Some street'
        }
    }
]

Wanted output:

[
    {
        Id: 1,
        Name: 'Customer1',
        AddressId: 1,
        Address : 
        {
            Id: 1,
            Street: 'Some street'
        }
    },
    {
        Id: 2,
        Name: 'Customer2',
        AddressId: null,
        Address : null
    }
]

The models above is an example. I actually got way bigger models, but I tried to keep the example as short as possible to provide a mcve . I've read this and this question, but I'm not getting any error. I just don't get the entities at all.

Answer 1

It appeared that the wanted output is the normal behavior for an OData service when using $expand . The error was caused by my mappings.

For some reason I had a bit of old code that made the Address required, even though the foreign key itself was nullable.

public class CustomerMap : EntityTypeConfiguration<Customer>
{
    public CustomerMap()
    {
        // Other code...

        // This is wrong!
        this.HasReguired(c => c.Address).WithMany(a => a.Customers);


        // This is right!
        this.HasOptional(c => c.Address).WithMany(a => a.Customers); 
    }
}

And because of the mapping, EF translated the SQL into an INNER JOIN instead of an OUTER JOIN .