LINQ Join返回IQueryable

Question

I've a relationship between 3 tables like this

I wanna have a method that given a parameter of type table1 and the DbContext I get all the related rows from table3 passing through table2

Here's my implementation

public static IQueryable<table3> GetRows(
  EntitiesContext context, 
  table1 row)
{
  var table3Rows =
    from t2 in row.table2
    join t3 in context.table3 on t2.IdTable3 equals t3.Id
    select t3;

  return table3Rows;
}

The problem with this approach is that I can't return table3Rows because it's IEnumerable not IQueryable .

Is there any workaround to return IQueryable when using join ?

I need IQueryable because I plan to do some other queries against the result.

Answer 1

You're not going to be able to use the navigation property if you have an already materialized Table1 object. If you have an IQueryable<Table1> then you can use the general approach you're using and the result will just naturally be an IQueryable<Table3> .

Since you have a materialized table row you'll need to query the DB for the Table2 items rather than using the navigation property.

public static IQueryable<table3> GetRows(
  EntitiesContext context, 
  table1 row)
{
  var table3Rows =
    from t2 in context.table2
    where row.Table2Id == t2.Id
    from t3 in t2.Table3 //here we can use a navigation property, since it's not on a materialized object.
    select t3;

  return table3Rows;
}