feat(spanner/spannertest): support JSON_VALUE function

spanner/spannertest/db.go

@@ -700,12 +700,20 @@ func (t *table) addColumn(cd spansql.ColumnDef, newTable bool) *status.Status {
 			// TODO: what happens in this case?
 			return status.Newf(codes.Unimplemented, "can't add NOT NULL columns to non-empty tables yet")
 		}
-		if cd.Generated != nil {
-			// TODO: should backfill the data to maintain behaviour with real spanner
-			return status.Newf(codes.Unimplemented, "can't add generated columns to non-empty tables yet")
-		}
 		for i := range t.rows {
-			t.rows[i] = append(t.rows[i], nil)
+			if cd.Generated != nil {
+				ec := evalContext{
+					cols: t.cols,
+					row:  t.rows[i],
+				}
+				val, err := ec.evalExpr(cd.Generated)
+				if err != nil {
+					return status.Newf(codes.InvalidArgument, "could not backfill values for generated column: %v", err)
+				}
+				t.rows[i] = append(t.rows[i], val)
+			} else {
+				t.rows[i] = append(t.rows[i], nil)
+			}
 		}
 	}
 

spanner/spannertest/db_test.go

@@ -441,8 +441,8 @@ func TestGeneratedColumn(t *testing.T) {
 	if err != nil {
 		t.Fatalf("%s: Bad DDL", err)
 	}
-	if st := db.ApplyDDL(ddl.List[0]); st.Code() == codes.OK {
-		t.Fatalf("Should have failed to add a generated column to non-empty table\n status: %v", st)
+	if st := db.ApplyDDL(ddl.List[0]); st.Code() != codes.OK {
+		t.Fatalf("Failed to add a generated column to non-empty table\n status: %v", st)
 	}
 
 }

spanner/spannertest/funcs.go

@@ -88,6 +88,25 @@ var functions = map[string]function{
 			return cast(values, types, true)
 		},
 	},
+	"JSON_VALUE": {
+		Eval: func(values []interface{}, types []spansql.Type) (interface{}, spansql.Type, error) {
+			if len(values) != 2 {
+				return nil, spansql.Type{}, status.Error(codes.InvalidArgument, "No matching signature for function JSON_VALUE for the given argument types")
+			}
+			if values[0] == nil || values[1] == nil {
+				return nil, spansql.Type{Base: spansql.String}, nil
+			}
+			_, okArg1 := values[0].(string)
+			_, okArg2 := values[1].(string)
+			if !(okArg1 && okArg2) {
+				return nil, spansql.Type{}, status.Error(codes.InvalidArgument, "No matching signature for function JSON_VALUE for the given argument types")
+			}
+			// This function currently has no implementation and always returns
+			// an empty string, as it would otherwise require an XPath query
+			// engine.
+			return "", spansql.Type{Base: spansql.String}, nil
+		},
+	},
 }
 
 func cast(values []interface{}, types []spansql.Type, safe bool) (interface{}, spansql.Type, error) {

spanner/spannertest/integration_test.go

@@ -1312,8 +1312,8 @@ func TestIntegration_GeneratedColumns(t *testing.T) {
 
 	err = updateDDL(t, adminClient,
 		`ALTER TABLE `+tableName+` ADD COLUMN TotalSales2 INT64 AS (NumSongs * EstimatedSales) STORED`)
-	if err == nil {
-		t.Fatalf("Should have failed to add a generated column to non empty table")
+	if err != nil {
+		t.Fatalf("Failed to add a generated column to a non-empty table: %v", err)
 	}
 
 	ri := client.Single().Query(ctx, spanner.NewStatement(

spanner/spansql/keywords.go

@@ -231,4 +231,7 @@ var allFuncs = []string{
 	"UNIX_MILLIS",
 	"UNIX_MICROS",
 	"PENDING_COMMIT_TIMESTAMP",
+
+	// JSON functions.
+	"JSON_VALUE",
 }

spanner/spansql/parser_test.go

@@ -862,6 +862,21 @@ func TestParseDDL(t *testing.T) {
 				},
 			},
 			}},
+		{`ALTER TABLE products ADD COLUMN item STRING(MAX) AS (JSON_VALUE(itemDetails, '$.itemDetails')) STORED`, &DDL{Filename: "filename", List: []DDLStmt{
+			&AlterTable{
+				Name: "products",
+				Alteration: AddColumn{Def: ColumnDef{
+					Name:     "item",
+					Type:     Type{Base: String, Len: MaxLen},
+					Position: line(1),
+					Generated: Func{
+						Name: "JSON_VALUE",
+						Args: []Expr{ID("itemDetails"), StringLiteral("$.itemDetails")},
+					},
+				}},
+				Position: line(1),
+			},
+		}}},
 	}
 	for _, test := range tests {
 		got, err := ParseDDL("filename", test.in)