feat: Add Unflatten tables method

schema/table.go

@@ -275,6 +275,31 @@ func (tt Tables) FlattenTables() Tables {
 	return slices.Clip(deduped)
 }
 
+// UnflattenTables returns a new Tables copy with the relations unflattened. This is the
+// opposite operation of FlattenTables.
+func (tt Tables) UnflattenTables() (Tables, error) {
+	tables := make(Tables, 0, len(tt))
+	for _, t := range tt {
+		table := *t
+		tables = append(tables, &table)
+	}
+	topLevel := make([]*Table, 0, len(tt))
+	// build relations
+	for _, table := range tables {
+		if table.Parent == nil {
+			topLevel = append(topLevel, table)
+			continue
+		}
+		parent := tables.Get(table.Parent.Name)
+		if parent == nil {
+			return nil, fmt.Errorf("parent table %s not found", table.Parent.Name)
+		}
+		table.Parent = parent
+		parent.Relations = append(parent.Relations, table)
+	}
+	return slices.Clip(topLevel), nil
+}
+
 func (tt Tables) TableNames() []string {
 	ret := []string{}
 	for _, t := range tt {

schema/table_test.go

@@ -16,6 +16,7 @@ var testTable = &Table{
 		{
 			Name:    "test2",
 			Columns: []Column{},
+			Parent:  &Table{Name: "test"},
 		},
 	},
 }
@@ -45,6 +46,15 @@ func TestTablesFlatten(t *testing.T) {
 	}
 }
 
+func TestTablesUnflatten(t *testing.T) {
+	srcTables := Tables{testTable}
+	tables, err := srcTables.FlattenTables().UnflattenTables()
+	require.NoError(t, err)
+	require.Equal(t, 1, len(srcTables)) // verify that the source Tables were left untouched
+	require.Equal(t, 1, len(tables))    // verify that the tables are equal to what we started with
+	require.Equal(t, 1, len(tables[0].Relations))
+}
+
 func TestTablesFilterDFS(t *testing.T) {
 	tests := []struct {
 		name                    string