dialect/sql/schema: add tables inspection capabilities (#1178)

dialect/sql/schema/inspect.go

@@ -0,0 +1,86 @@
+// Copyright 2019-present Facebook Inc. All rights reserved.
+// This source code is licensed under the Apache 2.0 license found
+// in the LICENSE file in the root directory of this source tree.
+
+package schema
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/facebook/ent/dialect"
+	"github.com/facebook/ent/dialect/sql"
+)
+
+// MigrateOption allows for managing schema configuration using functional options.
+type InspectOption func(inspect *Inspector)
+
+// WithSchema provides a schema (named-database) for reading the tables from.
+func WithSchema(schema string) InspectOption {
+	return func(m *Inspector) {
+		m.schema = schema
+	}
+}
+
+// An Inspector provides methods for inspecting database tables.
+type Inspector struct {
+	sqlDialect
+	schema string
+}
+
+// NewInspect returns an inspector for the given SQL driver.
+func NewInspect(d dialect.Driver, opts ...InspectOption) (*Inspector, error) {
+	i := &Inspector{}
+	for _, opt := range opts {
+		opt(i)
+	}
+	switch d.Dialect() {
+	case dialect.MySQL:
+		i.sqlDialect = &MySQL{Driver: d, schema: i.schema}
+	case dialect.SQLite:
+		i.sqlDialect = &SQLite{Driver: d}
+	case dialect.Postgres:
+		i.sqlDialect = &Postgres{Driver: d, schema: i.schema}
+	default:
+		return nil, fmt.Errorf("sql/schema: unsupported dialect %q", d.Dialect())
+	}
+	return i, nil
+}
+
+// Tables returns the tables in the schema.
+func (i *Inspector) Tables(ctx context.Context) ([]*Table, error) {
+	names, err := i.tables(ctx)
+	if err != nil {
+		return nil, err
+	}
+	tx := dialect.NopTx(i.sqlDialect)
+	tables := make([]*Table, 0, len(names))
+	for _, name := range names {
+		t, err := i.table(ctx, tx, name)
+		if err != nil {
+			return nil, err
+		}
+		tables = append(tables, t)
+	}
+	return tables, nil
+}
+
+func (i *Inspector) tables(ctx context.Context) ([]string, error) {
+	t, ok := i.sqlDialect.(interface{ tables() sql.Querier })
+	if !ok {
+		return nil, fmt.Errorf("sql/schema: %q driver does not support inspection", i.Dialect())
+	}
+	query, args := t.tables().Query()
+	var (
+		names []string
+		rows  = &sql.Rows{}
+	)
+	if err := i.Query(ctx, query, args, rows); err != nil {
+		return nil, fmt.Errorf("mysql: reading table names %w", err)
+	}
+	defer rows.Close()
+	if err := sql.ScanSlice(rows, &names); err != nil {
+		return nil, err
+	}
+	return names, nil
+}