Creating a self-referencing Many to Many relationship in Entity Framework 7
asp.net-core c# entity-framework entity-framework-core
Question
I'm attempting to set up my database using the Entity Framework 7 fluent API to add a self-referencing many-to-many relationship. The class in question looks like:
public class Definition
{
// Some properties
public virtual ICollection<Definition> AllowedChildDefinitions { get; set; }
}
where the intended relationship is that each definition can have an arbitrary amount of children, of any instance. I would expect a separate table with parent/child columns, where each parent can have multiple children, and each child can be on multiple parents.
There are examples of many-to-many, and examples of self-referencing tables, but I can't work out how to combine the two.
Popular Answer
The workaround is to map the join table to an entity. Please look into this.
public class Definition
{
public int Id { get; set; }
public ICollection<ChildrenDefinition> ChildrenDefinitions{ get; set; }
}
public class ChildrenDefinition
{
public int DefinitionId { get; set; }
public Definition Definition { get; set; }
public int ChildrenId { get; set; }
public Children Children { get; set; }
}
public class Children
{
public int Id { get; set; }
public ICollection<ChildrenDefinition> ChildrenDefinitions{ get; set; }
}
Be sure to configure ChildrenDefinition with a composite key:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<ChildrenDefinition>().HasKey(x => new { x.DefinitionId, x.ChildrenId });
}
To navigate, use a Select:
// Children.Definition
var definitions = Children.ChildrenDefinitions.Select(c => c.Definition);
Hope this may help you out!
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