"using both many-to-many and one-to-many to same entity" Code Answer

if you have more than one navigation property refering to the same entity ef does not know where the inverse navigation property on the other entity belongs to. in your example: does a.objectsofb refer to b.objecta or to b.otherobjectsofa? both would be possible and a valid model.

now, ef does not throw an exception like "cannot determine relationships unambiguously" or something. instead it decides that b.objecta refers to a third endpoint in b which is not exposed as navigation property in the model. this creates the first foreign key in table b. the two navigation properties in b refer to two endpoints in a which are also not exposed in the model: b.objecta creats the second foreign key in table b and b.otherobjectsofa creates a foreign key in table a.

to fix this you must specify the relationships explicitely.

option one (the easiest way) is to use the inverseproperty attribute:

public class a
{
    public int id { get; set; }
    public string name { get; set; }
    [inverseproperty("otherobjectsofa")]
    public virtual icollection<b> objectsofb { get; set; }
}

this defines that a.objectsofb is part of a many-to-many relation to b.otherobjectsofa.

the other option is to define the relationships completely in fluent api:

protected override void onmodelcreating(dbmodelbuilder modelbuilder)
{
    modelbuilder.entity<a>()
        .hasmany(a => a.objectsofb)
        .withmany(b => b.otherobjectsofa)
        .map(x =>
        {
            x.mapleftkey("aid");
            x.maprightkey("bid");
            x.totable("abs");
        });

    modelbuilder.entity<b>()
        .hasrequired(b => b.objecta)  // or hasoptional
        .withmany()
        .willcascadeondelete(false);  // not sure if necessary, you can try it
                                      // without if you want cascading delete
}