tenbits tenbits - 2 months ago 20
C# Question

EF: Create/Remove relation from Many-to-Many relations when `AutoDetectChangesEnabled` and `ProxyCreationEnabled` are disabled on DbContext


  1. Knowning
    Foo.Id
    and
    Bar.Id
    how can I create their relation without loading the entities from the DB.

    class Foo {
    public int Id { get; set; }
    public Lst<Bar> Bars { get; set; }
    }

    class Bar {
    public int Id { get; set; }
    public Lst<Foo> Foos { get; set; }
    }


    Also this configuration are disabled in
    DbContext
    constructor:

    Configuration.AutoDetectChangesEnabled = false;
    Configuration.ProxyCreationEnabled = false;
    Configuration.LazyLoadingEnabled = false;

  2. And how it is possible to remove the relationship?






Example:

using (var ctx = new DbCtx())
{
ctx.Configuration.LazyLoadingEnabled = false;
ctx.Configuration.ProxyCreationEnabled = false;
ctx.Configuration.AutoDetectChangesEnabled = false;
ctx.Database.Log += Console.WriteLine;

var foo = new Foo {Id = 1, Bars = new List<Bar>() };
var bar = new Bar { Id = 3, Foos = new List<Foo>() };

// This approach wont work, as AutoDetectChanges are disabled
ctx.Foos.Attach(foo);
ctx.Bars.Attach(bar);

foo.Bars.Add(bar);
ctx.SaveChanges();
}


How can I define relation here, without changing the configuration.

Thank you in advance.

Answer

Ok, have found the solution and here is the helper method:

static void ChangeRelationship<T1, T2>(
    IObjectContextAdapter ctx, 
    T1 a, 
    T2 b, 
    Expression<Func<T1, object>> getNavigationProperty,
    EntityState state) where T1: class
{
    ctx
        .ObjectContext
        .ObjectStateManager
        .ChangeRelationshipState(
            a,
            b,
            getNavigationProperty,
            state
        );
}

And using it in my example from the question:

using (var ctx = new DbCtx())
{
    ctx.Configuration.LazyLoadingEnabled = false;
    ctx.Configuration.ProxyCreationEnabled = false;
    ctx.Configuration.AutoDetectChangesEnabled = false;
    ctx.Database.Log += Console.WriteLine;

    var foo = new Foo {Id = 1, Bars = new List<Bar>()};
    var bar = new Bar { Id = 3, Foos = new List<Foo>() };

    ctx.Entry(foo).State = EntityState.Unchanged;
    ctx.Entry(bar).State = EntityState.Unchanged;

    // create
    ChangeRelationship(ctx, foo, bar, x => x.Bars, EntityState.Added);
    ctx.SaveChanges();

    // remove
    ChangeRelationship(ctx, foo, bar, x => x.Bars, EntityState.Deleted);
    ctx.SaveChanges();
}
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