updated postgres driver, add database.Error struct

Makefile

@@ -26,7 +26,7 @@ test-short:
 test:
 	@-rm -r .coverage
 	@mkdir .coverage
-	make test-with-flags TEST_FLAGS='-v -race -covermode atomic -coverprofile .coverage/_$$(RAND).txt  -bench=. -benchmem'
+	make test-with-flags TEST_FLAGS='-v -race -covermode atomic -coverprofile .coverage/_$$(RAND).txt -bench=. -benchmem'
 	@echo 'mode: atomic' > .coverage/combined.txt
 	@cat .coverage/*.txt | grep -v 'mode: atomic' >> .coverage/combined.txt
 

database/driver.go

@@ -51,6 +51,7 @@ type Driver interface {
 	// Lock should acquire a database lock so that only one migration process
 	// can run at a time. Migrate will call this function before Run is called.
 	// If the implementation can't provide this functionality, return nil.
+	// Return database.ErrLocked if database is already locked.
 	Lock() error
 
 	// Unlock should release the lock. Migrate will call this function after

database/error.go

@@ -0,0 +1,27 @@
+package database
+
+import (
+	"fmt"
+)
+
+// Error should be used for errors involving queries ran against the database
+type Error struct {
+	// Optional: the line number
+	Line uint
+
+	// Query is a query excerpt
+	Query []byte
+
+	// Err is a useful/helping error message for humans
+	Err string
+
+	// OrigErr is the underlying error
+	OrigErr error
+}
+
+func (e Error) Error() string {
+	if len(e.Err) == 0 {
+		return fmt.Sprintf("%v in line %v: %s", e.OrigErr, e.Line, e.Query)
+	}
+	return fmt.Sprintf("%v in line %v: %s (details: %v)", e.Err, e.Line, e.Query, e.OrigErr)
+}

database/postgres/postgres.go

@@ -16,13 +16,16 @@ func init() {
 	database.Register("postgres", &Postgres{})
 }
 
+var MigrationsTable = "schema_migrations"
+
 var (
 	ErrNilConfig      = fmt.Errorf("no config")
 	ErrNoDatabaseName = fmt.Errorf("no database name")
+	ErrNoSchema       = fmt.Errorf("no schema")
+	ErrDatabaseDirty  = fmt.Errorf("database is dirty")
 )
 
 type Config struct {
-	// DatbaseName is the name of the database
 	DatabaseName string
 }
 
@@ -31,10 +34,18 @@ func WithInstance(instance *sql.DB, config *Config) (database.Driver, error) {
 		return nil, ErrNilConfig
 	}
 
-	if len(config.DatabaseName) == 0 {
+	query := `SELECT CURRENT_DATABASE()`
+	var databaseName string
+	if err := instance.QueryRow(query).Scan(&databaseName); err != nil {
+		return nil, &database.Error{OrigErr: err, Query: []byte(query)}
+	}
+
+	if len(databaseName) == 0 {
 		return nil, ErrNoDatabaseName
 	}
 
+	config.DatabaseName = databaseName
+
 	px := &Postgres{
 		db:     instance,
 		config: config,
@@ -55,8 +66,6 @@ type Postgres struct {
 	config *Config
 }
 
-const tableName = "schema_migrations"
-
 func (p *Postgres) Open(url string) (database.Driver, error) {
 	purl, err := nurl.Parse(url)
 	if err != nil {
@@ -97,10 +106,12 @@ func (p *Postgres) Lock() error {
 		return err
 	}
 
-	//  It will either obtain the lock immediately and return true, or return false if the lock cannot be acquired immediately.
+	// This will either obtain the lock immediately and return true,
+	// or return false if the lock cannot be acquired immediately.
+	query := `SELECT pg_try_advisory_lock($1)`
 	var success bool
-	if err := p.db.QueryRow("SELECT pg_try_advisory_lock($1)", aid).Scan(&success); err != nil {
-		return err
+	if err := p.db.QueryRow(query, aid).Scan(&success); err != nil {
+		return &database.Error{OrigErr: err, Err: "try lock failed", Query: []byte(query)}
 	}
 
 	if success {
@@ -121,104 +132,168 @@ func (p *Postgres) Unlock() error {
 		return err
 	}
 
-	if _, err := p.db.Exec("SELECT pg_advisory_unlock($1)", aid); err != nil {
-		return err
+	query := `SELECT pg_advisory_unlock($1)`
+	if _, err := p.db.Exec(query, aid); err != nil {
+		return &database.Error{OrigErr: err, Query: []byte(query)}
 	}
 	p.isLocked = false
 	return nil
 }
 
 func (p *Postgres) Run(version int, migration io.Reader) error {
+	if dirty, err := p.isDirty(); err != nil {
+		return err
+	} else if dirty {
+		return ErrDatabaseDirty
+	}
+
 	if migration == nil {
 		// just apply version
-		return p.saveVersion(version)
+		return p.saveVersion(version, false)
 	}
 
-	mgr, err := ioutil.ReadAll(migration)
+	migr, err := ioutil.ReadAll(migration)
 	if err != nil {
 		return err
 	}
 
-	// it would be nice to be able to wrap the migration into the transaction, too
-	// unfortunately things like `CREATE INDEX CONCURRENTLY` aren't possible in a
-	// transaction. so if something fails between running the migration, and
-	// storing the latest migration version in the version table, we alert the user
-	// who then needs to manually fix.
-	// TODO: two phase commit?
-	if _, err := p.db.Exec(string(mgr[:])); err != nil {
+	// set dirty flag and set version
+	if err := p.saveVersion(version, true); err != nil {
 		return err
 	}
 
-	return p.saveVersion(version)
+	// run migration
+	query := string(migr[:])
+	if _, err := p.db.Exec(query); err != nil {
+		// TODO: cast to postgress error and get line number
+		return database.Error{OrigErr: err, Err: "migration failed", Query: migr}
+	}
+
+	// remove dirty flag
+	return p.saveVersion(version, false)
 }
 
-func (p *Postgres) saveVersion(version int) error {
+func (p *Postgres) saveVersion(version int, dirty bool) error {
 	tx, err := p.db.Begin()
 	if err != nil {
-		return err // TODO: warn user
+		return &database.Error{OrigErr: err, Err: "transaction start failed"}
 	}
 
-	if _, err := p.db.Exec("TRUNCATE " + tableName + ""); err != nil {
+	query := `TRUNCATE "` + MigrationsTable + `"`
+	if _, err := p.db.Exec(query); err != nil {
 		tx.Rollback()
-		return err // TODO: warn user
+		return &database.Error{OrigErr: err, Query: []byte(query)}
 	}
 
 	if version >= 0 {
-		if _, err := p.db.Exec("INSERT INTO "+tableName+" (version) VALUES ($1)", version); err != nil {
+		query = `INSERT INTO "` + MigrationsTable + `" (version, dirty) VALUES ($1, $2)`
+		if _, err := p.db.Exec(query, version, dirty); err != nil {
 			tx.Rollback()
-			return err // TODO: warn user
+			return &database.Error{OrigErr: err, Query: []byte(query)}
 		}
 	}
 
 	if err := tx.Commit(); err != nil {
-		return err // TODO: warn user
+		return &database.Error{OrigErr: err, Err: "transaction commit failed"}
 	}
 
 	return nil
 }
 
+func (p *Postgres) isDirty() (bool, error) {
+	query := `SELECT dirty FROM "` + MigrationsTable + `" LIMIT 1`
+	var dirty bool
+	err := p.db.QueryRow(query).Scan(&dirty)
+	switch {
+	case err == sql.ErrNoRows:
+		return false, nil
+
+	case err != nil:
+		if e, ok := err.(*pq.Error); ok {
+			if e.Code.Name() == "undefined_table" {
+				return false, nil
+			}
+		}
+		return false, &database.Error{OrigErr: err, Query: []byte(query)}
+
+	default:
+		return dirty, nil
+	}
+}
+
 func (p *Postgres) Version() (int, error) {
+	query := `SELECT version FROM "` + MigrationsTable + `" LIMIT 1`
 	var version uint64
-	err := p.db.QueryRow("SELECT version FROM " + tableName + " ORDER BY version DESC LIMIT 1").Scan(&version)
+	err := p.db.QueryRow(query).Scan(&version)
 	switch {
 	case err == sql.ErrNoRows:
 		return database.NilVersion, nil
+
 	case err != nil:
 		if e, ok := err.(*pq.Error); ok {
 			if e.Code.Name() == "undefined_table" {
 				return database.NilVersion, nil
 			}
 		}
-		return 0, err
+		return 0, &database.Error{OrigErr: err, Query: []byte(query)}
+
 	default:
 		return int(version), nil
 	}
 }
 
 func (p *Postgres) Drop() error {
-	if _, err := p.db.Exec("DROP SCHEMA public cascade "); err != nil {
-		return err
+	// select all tables in current schema
+	query := `SELECT table_name FROM information_schema.tables WHERE table_schema=(SELECT current_schema())`
+	tables, err := p.db.Query(query)
+	if err != nil {
+		return &database.Error{OrigErr: err, Query: []byte(query)}
 	}
-	if _, err := p.db.Exec("CREATE SCHEMA public"); err != nil {
-		return err
+	defer tables.Close()
+
+	// delete one table after another
+	tableNames := make([]string, 0)
+	for tables.Next() {
+		var tableName string
+		if err := tables.Scan(&tableName); err != nil {
+			return err
+		}
+		if len(tableName) > 0 {
+			tableNames = append(tableNames, tableName)
+		}
 	}
-	if err := p.ensureVersionTable(); err != nil {
-		return err
+
+	if len(tableNames) > 0 {
+		// delete one by one ...
+		for _, t := range tableNames {
+			query = `DROP TABLE IF EXISTS ` + t + ` CASCADE`
+			if _, err := p.db.Exec(query); err != nil {
+				return &database.Error{OrigErr: err, Query: []byte(query)}
+			}
+		}
+		if err := p.ensureVersionTable(); err != nil {
+			return err
+		}
 	}
+
 	return nil
 }
 
 func (p *Postgres) ensureVersionTable() error {
-	r := p.db.QueryRow("SELECT count(*) FROM information_schema.tables WHERE table_name = $1 AND table_schema = (SELECT current_schema())", tableName)
-	c := 0
-	if err := r.Scan(&c); err != nil {
-		return err
+	// check if migration table exists
+	var count int
+	query := `SELECT COUNT(1) FROM information_schema.tables WHERE table_name = $1 AND table_schema = (SELECT current_schema()) LIMIT 1`
+	if err := p.db.QueryRow(query, MigrationsTable).Scan(&count); err != nil {
+		return &database.Error{OrigErr: err, Query: []byte(query)}
 	}
-	if c > 0 {
+	if count == 1 {
 		return nil
 	}
-	if _, err := p.db.Exec("CREATE TABLE IF NOT EXISTS " + tableName + " (version bigint not null primary key);"); err != nil {
-		return err
+
+	// if not, create the empty migration table
+	query = `CREATE TABLE "` + MigrationsTable + `" (version bigint not null primary key, dirty boolean not null)`
+	if _, err := p.db.Exec(query); err != nil {
+		return &database.Error{OrigErr: err, Query: []byte(query)}
 	}
 	return nil
 }