func (b *Backend) AddFields(db *sql.DB, m driver.Model, prevTable *sql.Table, newTable *sql.Table, fields []*sql.Field) error { rewrite := false for _, v := range fields { if !b.canAddField(v) { rewrite = true break } } if rewrite { name := db.QuoteIdentifier(m.Table()) tmpName := fmt.Sprintf("%s_%s", m.Table(), stringutil.Random(8)) quotedTmpName := db.QuoteIdentifier(tmpName) createSql, err := newTable.SQL(db, b, m, tmpName) if err != nil { return err } if _, err := db.Exec(createSql); err != nil { return err } fieldNames := generic.Map(prevTable.Fields, func(f *sql.Field) string { return f.Name }).([]string) // The previous table might have fields that we're not part // of the new table. fieldSet := make(map[string]bool) for _, v := range newTable.Fields { fieldSet[v.Name] = true } fieldNames = generic.Filter(fieldNames, func(n string) bool { return fieldSet[n] }).([]string) sqlFields := strings.Join(generic.Map(fieldNames, db.QuoteIdentifier).([]string), ", ") copySql := fmt.Sprintf("INSERT INTO %s (%s) SELECT %s FROM %s", quotedTmpName, sqlFields, sqlFields, name) if _, err := db.Exec(copySql); err != nil { return err } if _, err := db.Exec(fmt.Sprintf("DROP TABLE %s", name)); err != nil { return err } if _, err := db.Exec(fmt.Sprintf("ALTER TABLE %s RENAME TO %s", quotedTmpName, name)); err != nil { return err } return nil } return b.SqlBackend.AddFields(db, m, prevTable, newTable, fields) }
func ExampleFilter_even() { in := []int{1, 2, 3, 4} out := generic.Filter(in, func(a int) bool { return a%2 == 0 }).([]int) fmt.Println(out) // Output: [2 4] }