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project.go
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project.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 stages
import (
"context"
"github.com/FerretDB/FerretDB/internal/handlers/common"
"github.com/FerretDB/FerretDB/internal/handlers/common/aggregations"
"github.com/FerretDB/FerretDB/internal/handlers/common/aggregations/stages/projection"
"github.com/FerretDB/FerretDB/internal/handlers/commonerrors"
"github.com/FerretDB/FerretDB/internal/types"
"github.com/FerretDB/FerretDB/internal/util/iterator"
)
// project represents $project stage.
//
// {
// $project: {
// <output field1>: <expression1>,
// ...
// <output fieldN>: <expressionN>
// }
type project struct {
projection *types.Document
inclusion bool
}
// newProject validates projection document and creates a new $project stage.
func newProject(stage *types.Document) (aggregations.Stage, error) {
fields, err := common.GetRequiredParam[*types.Document](stage, "$project")
if err != nil {
return nil, commonerrors.NewCommandErrorMsgWithArgument(
commonerrors.ErrProjectBadExpression,
"$project specification must be an object",
"$project (stage)",
)
}
validated, inclusion, err := projection.ValidateProjection(fields)
if err != nil {
return nil, err
}
return &project{
projection: validated,
inclusion: inclusion,
}, nil
}
// Process implements Stage interface.
//
//nolint:lll // for readability
func (p *project) Process(_ context.Context, iter types.DocumentsIterator, closer *iterator.MultiCloser) (types.DocumentsIterator, error) {
return projection.ProjectionIterator(iter, closer, p.projection)
}
// check interfaces
var (
_ aggregations.Stage = (*project)(nil)
)