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 +14,97 @@
 
 package common
 
-import "github.com/FerretDB/FerretDB/internal/types"
+import (
+	"github.com/FerretDB/FerretDB/internal/types"
+	"github.com/FerretDB/FerretDB/internal/util/lazyerrors"
+)
+
+// isProjectionInclusion: projection can be only inclusion or exlusion. Validate and return true if inclusion.
+// Exception for the _id field
+func isProjectionInclusion(projection *types.Document) (inclusion bool, err error) {
+	errMsg := "projection must contain only inclusions or exclusions"
+	var exclusion bool
+	for k, v := range projection.Map() {
+		if k == "_id" { // _id is a special case and can be both
+			continue
+		}
+		switch v := v.(type) {
+		case bool:
+			if v {
+				if exclusion {
+					err = lazyerrors.New(errMsg)
+					return
+				}
+				inclusion = true
+			} else {
+				if inclusion {
+					err = lazyerrors.New(errMsg)
+					return
+				}
+				exclusion = true
+			}
+		case int32, int64, float64:
+			if compareScalars(v, int32(0)) == equal {
+				if inclusion {
+					err = lazyerrors.New(errMsg)
+					return
+				}
+				exclusion = true
+			} else {
+				if exclusion {
+					err = lazyerrors.New(errMsg)
+					return
+				}
+				inclusion = true
+			}
+		default:
+			err = lazyerrors.Errorf("unsupported operation %s %v (%T)", k, v, v)
+			return
+		}
+	}
+	return
+}
 
 // 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
+	}
+
+	inclusion, err := isProjectionInclusion(projection)
+	if err != nil {
+		return err
+	}
+
+	projectionMap := projection.Map()
+	for i := 0; i < len(docs); i++ {
+		for k := range docs[i].Map() {
+
+			v, ok := projectionMap[k]
+			if !ok {
+				if k == "_id" { // if _id is not in projection map, do not do anything with it
+					continue
+				}
+				if inclusion {
+					docs[i].Remove(k)
+				}
+				continue
+			}
+
+			switch v := v.(type) { // found in the projection
+			case bool:
+				if !v {
+					docs[i].Remove(k)
+				}
+			case int32, int64, float64:
+				if compareScalars(v, int32(0)) == equal {
+					docs[i].Remove(k)
+				}
+			default:
+				return lazyerrors.Errorf("unsupported operation %s %v (%T)", k, v, v)
+			}
+		}
+	}
+
 	return nil
 }

internal/handlers/handler_test.go

@@ -810,12 +810,12 @@ func TestReadOnlyHandlers(t *testing.T) {
 			},
 		},
 
-		"FindProjectionActorsFirstAndLastName": {
+		"FindProjectionInclusions": {
 			req: types.MustNewDocument(
 				"find", "actor",
 				"projection", types.MustNewDocument(
-					"first_name", int32(1),
 					"last_name", int32(1),
+					"last_update", true,
 				),
 				"filter", types.MustNewDocument(
 					"actor_id", int32(28),
@@ -826,8 +826,73 @@ 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),
+					"ns", "", // set by compareFunc
+				),
+				"ok", float64(1),
+			),
+			compareFunc: func(t testing.TB, _, expected, actual *types.Document) {
+				actualV := testutil.GetByPath(t, actual, "cursor", "ns")
+				testutil.SetByPath(t, expected, actualV, "cursor", "ns")
+				assert.Equal(t, expected, actual)
+			},
+		},
+
+		"FindProjectionExclusions": {
+			req: types.MustNewDocument(
+				"find", "actor",
+				"projection", types.MustNewDocument(
+					"first_name", int32(0),
+					"actor_id", false,
+				),
+				"filter", types.MustNewDocument(
+					"actor_id", int32(28),
+				),
+			),
+			reqSetDB: true,
+			resp: types.MustNewDocument(
+				"cursor", types.MustNewDocument(
+					"firstBatch", types.MustNewArray(
+						types.MustNewDocument(
+							"_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),
+					"ns", "", // set by compareFunc
+				),
+				"ok", float64(1),
+			),
+			compareFunc: func(t testing.TB, _, expected, actual *types.Document) {
+				actualV := testutil.GetByPath(t, actual, "cursor", "ns")
+				testutil.SetByPath(t, expected, actualV, "cursor", "ns")
+				assert.Equal(t, expected, actual)
+			},
+		},
+
+		"FindProjectionIDInclusion": {
+			req: types.MustNewDocument(
+				"find", "actor",
+				"projection", types.MustNewDocument(
+					"_id", false,
+					"actor_id", int32(1),
+				),
+				"filter", types.MustNewDocument(
+					"actor_id", int32(28),
+				),
+			),
+			reqSetDB: true,
+			resp: types.MustNewDocument(
+				"cursor", types.MustNewDocument(
+					"firstBatch", types.MustNewArray(
+						types.MustNewDocument(
+							"actor_id", int32(28),
 						),
 					),
 					"id", int64(0),