Add dump command (#23)

Adds `dbmate dump` command to write the database schema to a file.

The intent is for this file to be checked in to the codebase, similar to Rails' `schema.rb` (or `structure.sql`) file. This allows developers to share a single file documenting the database schema, and makes it considerably easier to review PRs which add (or change) migrations.

The existing `up`, `migrate`, and `rollback` commands will automatically trigger a schema dump, unless `--no-dump-schema` is passed.

Closes https://github.com/amacneil/dbmate/issues/5

pkg/dbmate/sqlite.go

@@ -1,11 +1,13 @@
 package dbmate
 
 import (
+	"bytes"
 	"database/sql"
 	"fmt"
 	"net/url"
 	"os"
 	"regexp"
+	"strings"
 
 	_ "github.com/mattn/go-sqlite3" // sqlite driver for database/sql
 )
@@ -56,6 +58,44 @@ func (drv SQLiteDriver) DropDatabase(u *url.URL) error {
 	return os.Remove(path)
 }
 
+func sqliteSchemaMigrationsDump(db *sql.DB) ([]byte, error) {
+	// load applied migrations
+	migrations, err := queryColumn(db,
+		"select quote(version) from schema_migrations order by version asc")
+	if err != nil {
+		return nil, err
+	}
+
+	// build schema_migrations table data
+	var buf bytes.Buffer
+	buf.WriteString("-- Dbmate schema migrations\n")
+
+	if len(migrations) > 0 {
+		buf.WriteString("INSERT INTO schema_migrations (version) VALUES\n  (" +
+			strings.Join(migrations, "),\n  (") +
+			");\n")
+	}
+
+	return buf.Bytes(), nil
+}
+
+// DumpSchema returns the current database schema
+func (drv SQLiteDriver) DumpSchema(u *url.URL, db *sql.DB) ([]byte, error) {
+	path := sqlitePath(u)
+	schema, err := runCommand("sqlite3", path, ".schema")
+	if err != nil {
+		return nil, err
+	}
+
+	migrations, err := sqliteSchemaMigrationsDump(db)
+	if err != nil {
+		return nil, err
+	}
+
+	schema = append(schema, migrations...)
+	return trimLeadingSQLComments(schema)
+}
+
 // DatabaseExists determines whether the database exists
 func (drv SQLiteDriver) DatabaseExists(u *url.URL) (bool, error) {
 	_, err := os.Stat(sqlitePath(u))
@@ -71,8 +111,8 @@ func (drv SQLiteDriver) DatabaseExists(u *url.URL) (bool, error) {
 
 // CreateMigrationsTable creates the schema_migrations table
 func (drv SQLiteDriver) CreateMigrationsTable(db *sql.DB) error {
-	_, err := db.Exec(`create table if not exists schema_migrations (
-		version varchar(255) primary key)`)
+	_, err := db.Exec("create table if not exists schema_migrations " +
+		"(version varchar(255) primary key)")
 
 	return err
 }