Revert "Revert Implemented IN case"

This reverts commit da759ab.

Author: Viktor Tochonov

src/FSharp.Data.GraphQL.Server.Middleware/ObjectListFilter.fs

@@ -13,6 +13,7 @@ type ObjectListFilter =
     | Equals of FieldFilter<System.IComparable>
     | GreaterThan of FieldFilter<System.IComparable>
     | LessThan of FieldFilter<System.IComparable>
+    | In of FieldFilter<System.IComparable list>
     | StartsWith of FieldFilter<string>
     | EndsWith of FieldFilter<string>
     | Contains of FieldFilter<string>
@@ -177,6 +178,11 @@ module ObjectListFilter =
                 Expression.Call (getEnumerableContainsMethod field.FieldType, Expression.PropertyOrField (param, f.FieldName), Expression.Constant (f.Value))
             | _ ->
                 Expression.Call (``member``, StringContainsMethod, Expression.Constant (f.Value))
+        | In f ->
+            let ``member`` = Expression.PropertyOrField (param, f.FieldName)
+            let values = f.Value |> List.map (fun v -> Expression.Equal(``member``, Expression.Constant(v)))
+            (values |> List.reduce (fun acc expr -> Expression.OrElse(acc, expr))) :> Expression
+
         | OfTypes types ->
             types
             |> Seq.map (fun t -> buildTypeDiscriminatorCheck param t)

tests/FSharp.Data.GraphQL.Tests/ObjectListFilterLinqTests.fs

@@ -119,6 +119,40 @@ let ``ObjectListFilter works with OR operator``() =
     result.Contact  |> equals { Email = "[email protected]" }
     result.Friends  |> equals [ { Email = "[email protected]" }; { Email = "[email protected]" } ]
 
+[<Fact>]
+let ``ObjectListFilter works with IN operator for string type field``() =
+    let filter =
+        In { FieldName = "firstName"; Value = ["Jeneffer"; "Ben"] }
+    let queryable = data.AsQueryable()
+    let filteredData = queryable.Apply(filter) |> Seq.toList
+    List.length filteredData |> equals 2
+    let result = List.head filteredData
+    result.ID |> equals 4
+    result.FirstName |> equals "Ben"
+    result.LastName |> equals "Adams"
+    result.Contact  |> equals { Email = "[email protected]" }
+    result.Friends  |> equals [ { Email = "[email protected]" }; { Email = "[email protected]" } ]
+    let result2 = List.last filteredData
+    result2.ID |> equals 7
+    result2.FirstName |> equals "Jeneffer"
+    result2.LastName |> equals "Trif"
+    result2.Contact |> equals { Email = "[email protected]" }
+    result2.Friends |> equals [ { Email = "[email protected]" } ]
+
+[<Fact>]
+let ``ObjectListFilter works with IN operator for int type field``() =
+    let filter =
+        In { FieldName = "id"; Value = [4; 2; 7] }
+    let queryable = data.AsQueryable()
+    let filteredData = queryable.Apply(filter) |> Seq.toList
+    List.length filteredData |> equals 3
+    let result = List.head filteredData
+    result.ID |> equals 4
+    result.FirstName |> equals "Ben"
+    result.LastName |> equals "Adams"
+    result.Contact  |> equals { Email = "[email protected]" }
+    result.Friends  |> equals [ { Email = "[email protected]" }; { Email = "[email protected]" } ]
+
 [<Fact>]
 let ``ObjectListFilter works with FilterField operator``() =
     let filter =