refactor: Remove database/sql from Driver interface

Just realized that the core godfish library code doesn't even need to
use the database/sql.DB connection. Removing this dependency frees up
the library to work with other databases that may not implement the
database/sql/driver.Driver interface at all.

driver.go

@@ -1,21 +1,13 @@
 package godfish
 
-import "database/sql"
-
-// A Driver describes what a database driver (anything at
-// https:/golang/go/wiki/SQLDrivers) should be able to do.
+// Driver adapts a database implementation to use godfish.
 type Driver interface {
  // Name should return the name of the driver: ie: postgres, mysql, etc
  Name() string
 
- // Connect should open a connection (a *sql.DB) to the database and save an
- // internal reference to that connection for later use. This library might
- // call this method multiple times, so use the internal reference if it's
- // present instead of reconnecting to the database.
- Connect(dsn string) (*sql.DB, error)
- // Close should check if there's an internal reference to a database
- // connection (a *sql.DB) and if it's present, close it. Then reset the
- // internal reference to that connection to nil.
+ // Connect should open a connection to the database.
+ Connect(dsn string) error
+ // Close should close the database connection.
  Close() error
 
  // AppliedVersions queries the schema migrations table for migration
@@ -47,5 +39,3 @@ type AppliedVersions interface {
  Next() bool
  Scan(dest ...interface{}) error
 }
-
-var _ AppliedVersions = (*sql.Rows)(nil)

drivers/mysql/mysql.go

@@ -19,12 +19,12 @@ type driver struct {
 }
 
 func (d *driver) Name() string { return "mysql" }
-func (d *driver) Connect(dsn string) (conn *sql.DB, err error) {
+func (d *driver) Connect(dsn string) (err error) {
  if d.connection != nil {
- conn = d.connection
  return
  }
- if conn, err = sql.Open(d.Name(), dsn); err != nil {
+ conn, err := sql.Open(d.Name(), dsn)
+ if err != nil {
  return
  }
  d.connection = conn

drivers/postgres/postgres.go

@@ -16,12 +16,12 @@ type driver struct {
 }
 
 func (d *driver) Name() string { return "postgres" }
-func (d *driver) Connect(dsn string) (conn *sql.DB, err error) {
+func (d *driver) Connect(dsn string) (err error) {
  if d.connection != nil {
- conn = d.connection
  return
  }
- if conn, err = sql.Open(d.Name(), dsn); err != nil {
+ conn, err := sql.Open(d.Name(), dsn)
+ if err != nil {
  return
  }
  d.connection = conn

godfish.go

@@ -21,7 +21,7 @@ func Migrate(driver Driver, directoryPath string, direction Direction, finishAtV
  if dsn, err = getDSN(); err != nil {
  return
  }
- if _, err = driver.Connect(dsn); err != nil {
+ if err = driver.Connect(dsn); err != nil {
  return
  }
  defer driver.Close()
@@ -72,7 +72,7 @@ func ApplyMigration(driver Driver, directoryPath string, direction Direction, ve
  if dsn, err = getDSN(); err != nil {
  return
  }
- if _, err = driver.Connect(dsn); err != nil {
+ if err = driver.Connect(dsn); err != nil {
  return
  }
  defer driver.Close()
@@ -201,7 +201,7 @@ func CreateSchemaMigrationsTable(driver Driver) (err error) {
  if dsn, err = getDSN(); err != nil {
  return
  }
- if _, err = driver.Connect(dsn); err != nil {
+ if err = driver.Connect(dsn); err != nil {
  return err
  }
  defer driver.Close()
@@ -214,7 +214,7 @@ func Info(driver Driver, directoryPath string, direction Direction, finishAtVers
  if dsn, err = getDSN(); err != nil {
  return
  }
- if _, err = driver.Connect(dsn); err != nil {
+ if err = driver.Connect(dsn); err != nil {
  return err
  }
  defer driver.Close()

godfish_test.go

@@ -1,6 +1,7 @@
 package godfish_test
 
 import (
+ "database/sql"
  "encoding/json"
  "os"
  "testing"
@@ -67,3 +68,12 @@ func TestInit(t *testing.T) {
  )
  }
 }
+
+func TestAppliedVersions(t *testing.T) {
+ // Regression test on the API. It's supposed to wrap this type from the
+ // standard library for the most common cases.
+ var thing interface{} = new(sql.Rows)
+ if _, ok := thing.(godfish.AppliedVersions); !ok {
+ t.Fatalf("expected %T to implement godfish.AppliedVersions", thing)
+ }
+}

internal/stub/driver.go

@@ -2,25 +2,23 @@
 package stub
 
 import (
- "database/sql"
  "fmt"
  "strings"
 
  "github.com/rafaelespinoza/godfish"
 )
 
 type Driver struct {
- connection *sql.DB
  appliedVersions godfish.AppliedVersions
  err error
  errorOnExecute error
 }
 
 var _ godfish.Driver = (*Driver)(nil)
 
-func (d *Driver) Name() string  { return "stub" }
-func (d *Driver) Connect(dsn string) (*sql.DB, error) { return d.connection, d.err }
-func (d *Driver) Close() error  { return d.err }
+func (d *Driver) Name() string { return "stub" }
+func (d *Driver) Connect(dsn string) error { return d.err }
+func (d *Driver) Close() error { return d.err }
 func (d *Driver) CreateSchemaMigrationsTable() error {
  if d.appliedVersions == nil {
  d.appliedVersions = MakeAppliedVersions()

internal/test.go

@@ -615,7 +615,7 @@ func setup(driver godfish.Driver, testName string, stubs []testDriverStub, migra
 // teardown clears state after running a test.
 func teardown(driver godfish.Driver, path string, tablesToDrop ...string) {
  var err error
- if _, err = driver.Connect(mustDSN()); err != nil {
+ if err = driver.Connect(mustDSN()); err != nil {
  panic(err)
  }
 
@@ -811,7 +811,7 @@ func generateMigrationFiles(pathToTestDir string, stubs []testDriverStub) error
 func collectAppliedVersions(driver godfish.Driver) (out []string, err error) {
  // Collect output of AppliedVersions.
  // Reconnect here because ApplyMigration closes the connection.
- if _, err = driver.Connect(mustDSN()); err != nil {
+ if err = driver.Connect(mustDSN()); err != nil {
  return
  }
  defer driver.Close()