Allow the /{db}/_index endpoint to accept jq definitions

We currently have to create jq-based indexes by writing out the whole
design document containing the Mango index definition, because the
`/{db}/_index` endpoint does not except anything except "asc" or "desc"
next to field names in the sort syntax.

Here we expand this to allow { "$jq": "..." } as well, letting us create
jq-based indexes without knowing the internal document format.

Even though internally we support mixing jq expressions with normal
field lookups in multi-field indexes, for now I'm restricting this so
that multi-field indexes have to either all use the same sort direction,
or all be jq expressions.

src/mango/src/mango_sort.erl

@@ -49,20 +49,24 @@ sort_field({[{Name, <<"asc">>}]}) when is_binary(Name) ->
     {Name, <<"asc">>};
 sort_field({[{Name, <<"desc">>}]}) when is_binary(Name) ->
     {Name, <<"desc">>};
+sort_field({[{Name, {[{<<"$jq">>, Expr}]} = Jq}]}) when is_binary(Name) and is_binary(Expr) ->
+    {Name, Jq};
 sort_field({Name, BadDir}) when is_binary(Name) ->
     ?MANGO_ERROR({invalid_sort_dir, BadDir});
 sort_field(Else) ->
     ?MANGO_ERROR({invalid_sort_field, Else}).
 
 validate({Props}) ->
-    % Assert each field is in the same direction
-    % until we support mixed direction sorts.
-    Dirs = [D || {_, D} <- Props],
+    % Assert each field is in the same direction, or all fields are jq
+    % expressions, until we support mixed direction sorts.
+    Dirs = lists:map(fun(Prop) ->
+        case Prop of
+            {_, {[{<<"$jq">>, _}]}} -> jq;
+            {_, D} -> D
+        end
+    end, Props),
     case lists:usort(Dirs) of
-        [] ->
-            ok;
-        [_] ->
-            ok;
-        _ ->
-            ?MANGO_ERROR({unsupported, mixed_sort})
+        [] -> ok;
+        [_] -> ok;
+        _ -> ?MANGO_ERROR({unsupported, mixed_sort})
     end.

src/mango/test/22-index-function-test.py

@@ -13,44 +13,22 @@
 import mango
 
 
-def create_index(db, ddoc_id, view_id, definition):
-    db.save_docs(
-        [
-            {
-                "_id": ddoc_id,
-                "language": "query",
-                "views": {
-                    view_id: {
-                        "map": {"fields": definition, "partial_filter_selector": {}},
-                        "reduce": "_count",
-                        "options": {"def": {"fields": definition}},
-                    }
-                },
-            }
-        ]
-    )
-
-
 class IndexFunctionTests(mango.DbPerClass):
     @classmethod
     def setUpClass(klass):
         super(IndexFunctionTests, klass).setUpClass()
 
-        create_index(
-            klass.db,
-            "_design/jq-split-1",
-            "jq-json-index",
-            {"f1_words": {"$jq": '.f1 | split(" ") | .[]'}},
+        klass.db.create_index(
+            [
+                {"f1_words": {"$jq": '.f1 | split(" ") | .[]'}},
+            ]
         )
 
-        create_index(
-            klass.db,
-            "_design/jq-split-2",
-            "jq-json-index",
-            {
-                "f2_words": {"$jq": '.f2 | split(" ") | .[]'},
-                "f3_words": {"$jq": '.f3 | split(" ") | .[]'},
-            },
+        klass.db.create_index(
+            [
+                {"f2_words": {"$jq": '.f2 | split(" ") | .[]'}},
+                {"f3_words": {"$jq": '.f3 | split(" ") | .[]'}},
+            ],
         )
 
         klass.db.save_docs(