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]
}