Projection: <field>: <1 or true> and <field>: <0 or false>

.gitignore

@@ -4,6 +4,7 @@
 /bin/
 /vendor/
 cover.txt
+cover.html
 old.txt
 new.txt
 

internal/handlers/common/projection.go

@@ -14,10 +14,47 @@
 
 package common
 
-import "github.com/FerretDB/FerretDB/internal/types"
+import (
+	"github.com/FerretDB/FerretDB/internal/types"
+	"github.com/FerretDB/FerretDB/internal/util/lazyerrors"
+)
 
 // ProjectDocuments modifies given documents in places according to the given projection.
 func ProjectDocuments(docs []*types.Document, projection *types.Document) error {
-	// TODO
+	if projection.Len() == 0 {
+		return nil
+	}
+	projectionMap := projection.Map()
+	for i := 0; i < len(docs); i++ {
+		for k := range docs[i].Map() {
+			if k == "_id" {
+				continue
+			}
+
+			v, ok := projectionMap[k]
+			if !ok {
+				docs[i].Remove(k)
+				continue
+			}
+
+			switch v := v.(type) {
+			case bool:
+				if !v {
+					docs[i].Remove(k)
+					continue
+				}
+				continue
+
+			case int32, int64, float32, float64:
+				if compareScalars(v, int32(0)) == equal {
+					docs[i].Remove(k)
+					continue
+				}
+			default:
+				return lazyerrors.Errorf("unsupported operation {%v %v}", k, v)
+			}
+		}
+	}
+
 	return nil
 }

internal/handlers/handler_test.go

@@ -810,12 +810,14 @@ func TestReadOnlyHandlers(t *testing.T) {
 			},
 		},
 
-		"FindProjectionActorsFirstAndLastName": {
+		"FindProjectionField": {
 			req: types.MustNewDocument(
 				"find", "actor",
 				"projection", types.MustNewDocument(
-					"first_name", int32(1),
+					"first_name", int32(0),
 					"last_name", int32(1),
+					"last_update", true,
+					"actor_id", false,
 				),
 				"filter", types.MustNewDocument(
 					"actor_id", int32(28),
@@ -826,8 +828,9 @@ func TestReadOnlyHandlers(t *testing.T) {
 				"cursor", types.MustNewDocument(
 					"firstBatch", types.MustNewArray(
 						types.MustNewDocument(
-							"first_name", "WOODY",
+							"_id", types.ObjectID{0x61, 0x2e, 0xc2, 0x80, 0x00, 0x00, 0x00, 0x1c, 0x00, 0x00, 0x00, 0x1c},
 							"last_name", "HOFFMAN",
+							"last_update", time.Date(2020, 2, 15, 9, 34, 33, 0, time.UTC).Local(),
 						),
 					),
 					"id", int64(0),