/
pushdown.go
74 lines (59 loc) · 1.93 KB
/
pushdown.go
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// Copyright 2021 FerretDB Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package aggregations
import (
"github.com/FerretDB/FerretDB/internal/types"
"github.com/FerretDB/FerretDB/internal/util/must"
)
// GetPushdownQuery gets pushdown query ($match and $sort) for aggregation.
//
// If the first two stages are either $match, $sort, or a combination of them, we can push them down.
// In this case, we return the first match and sort statements to pushdown.
// If $match stage is not present, match is returned as nil.
// If $sort stage is not present, sort is returned as nil.
func GetPushdownQuery(stagesDocs []any) (match *types.Document, sort *types.Document) {
if len(stagesDocs) == 0 {
return
}
stagesToPushdown := []any{stagesDocs[0]}
if len(stagesDocs) > 1 {
stagesToPushdown = append(stagesToPushdown, stagesDocs[1])
}
for _, s := range stagesToPushdown {
stage, isDoc := s.(*types.Document)
if !isDoc {
return nil, nil
}
switch {
case stage.Has("$match"):
matchQuery := must.NotFail(stage.Get("$match"))
query, isDoc := matchQuery.(*types.Document)
if !isDoc || match != nil {
continue
}
match = query
case stage.Has("$sort"):
sortQuery := must.NotFail(stage.Get("$sort"))
query, isDoc := sortQuery.(*types.Document)
if !isDoc || sort != nil {
continue
}
sort = query
default:
// not $match nor $sort, we shouldn't continue pushdown
return
}
}
return
}