[ACCEPTED]-How to create a dynamic LINQ join extension method-linq-to-objects

Accepted answer
Score: 26

I've fixed it myself now. It was a schoolboy 6 error passing too many parameters to the 5 CreateQuery(... ) call. Paste the following 4 code into the Dynamic.cs file within the 3 DynamicQueryable class for a dynamic Join 2 extension method. You can find the source 1 for the DynamicQuery sample project at http://code.msdn.microsoft.com/csharpsamples.

    public static IQueryable Join(this IQueryable outer, IEnumerable inner, string outerSelector, string innerSelector, string resultsSelector, params object[] values)
        if (inner == null) throw new ArgumentNullException("inner");
        if (outerSelector == null) throw new ArgumentNullException("outerSelector");
        if (innerSelector == null) throw new ArgumentNullException("innerSelector");
        if (resultsSelector == null) throw new ArgumentNullException("resultsSelctor");

        LambdaExpression outerSelectorLambda = DynamicExpression.ParseLambda(outer.ElementType, null, outerSelector, values);
        LambdaExpression innerSelectorLambda = DynamicExpression.ParseLambda(inner.AsQueryable().ElementType, null, innerSelector, values);

        ParameterExpression[] parameters = new ParameterExpression[] {
            Expression.Parameter(outer.ElementType, "outer"), Expression.Parameter(inner.AsQueryable().ElementType, "inner") };
        LambdaExpression resultsSelectorLambda = DynamicExpression.ParseLambda(parameters, null, resultsSelector, values);

        return outer.Provider.CreateQuery(
                typeof(Queryable), "Join",
                new Type[] {outer.ElementType, inner.AsQueryable().ElementType, outerSelectorLambda.Body.Type, resultsSelectorLambda.Body.Type  },
                outer.Expression, inner.AsQueryable().Expression, Expression.Quote(outerSelectorLambda), Expression.Quote(innerSelectorLambda), Expression.Quote(resultsSelectorLambda)));

    //The generic overload.
    public static IQueryable<T> Join<T>(this IQueryable<T> outer, IEnumerable<T> inner, string outerSelector, string innerSelector, string resultsSelector, params object[] values)
        return (IQueryable<T>)Join((IQueryable)outer, (IEnumerable)inner, outerSelector, innerSelector, resultsSelector, values);
Score: 4

You can install the nuget package of System.Linq.Dynamic.Core 9 - https://github.com/StefH/System.Linq.Dynamic.Core

This has the join method implemented 8 along with various other helper methods.

Using 7 this library you can do a simple join in 6 the following the way


in the result selector 5 outer and inner are key words to access the result 4 of the join.

Using a key with multiple properties 3 and/or selecting a result with multiple 2 properties can be done in the following 1 way

myContext.TableA.Join(myContext.TableB,'new (Id as key1,Code as key2)','new (TableAId as key1,AnotherCol as key2)','new(outer.Id,inner.Desc)',null)

Score: 1

Here is some sample code showing a join 3 on multiple columns. Using a datatable and 2 datarows you need to always access fields 1 via the indexer.

  DataTable t1 = new DataTable();
  t1.Columns.Add("FundId", typeof(int));
  t1.Columns.Add("Date", typeof(DateTime));
  t1.Columns.Add("CodeA", typeof(string));
  t1.Rows.Add(1, new DateTime(2010, 01, 01), "A1");
  t1.Rows.Add(2, new DateTime(2010, 01, 01), "A2");
  t1.Rows.Add(3, new DateTime(2010, 01, 01), "A3");

  DataTable t2 = new DataTable();
  t2.Columns.Add("FundId", typeof(int));
  t2.Columns.Add("Date", typeof(DateTime));
  t2.Columns.Add("CodeB", typeof(string));
  t2.Rows.Add(1, new DateTime(2010, 01, 01), "B1");
  t2.Rows.Add(2, new DateTime(2010, 01, 01), "B2");
  t2.Rows.Add(3, new DateTime(2010, 01, 01), "B3");

  IQueryable outerTable = t1.AsEnumerable().AsQueryable();
  IEnumerable innerTable = t2.AsEnumerable();

  var query = outerTable.Join
      "new(get_Item(0) as FundId, get_Item(1) as Date)",
      "new(get_Item(0) as FundId, get_Item(1) as Date)",
      "new(outer.get_Item(0) as FundId, outer.get_Item(2) as CodeA, inner.get_Item(2) as CodeB)"

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