package dbtools import ( "context" "errors" "fmt" "github.com/rs/zerolog/log" "gogs.mikescher.com/BlackForestBytes/goext/langext" "gogs.mikescher.com/BlackForestBytes/goext/sq" "regexp" "strings" "sync" ) // // This is..., not good... // // for sq.ScanAll to work with (left-)joined tables _need_ to get column names aka "alias.column" // But sqlite (and all other db server) only return "column" if we don't manually specify `alias.column as "alias.columnname"` // But always specifying all columns (and their alias) would be __very__ cumbersome... // // The "solution" is this preprocessor, which translates queries of the form `SELECT tab1.*, tab2.* From tab1` into `SELECT tab1.col1 AS "tab1.col1", tab1.col2 AS "tab1.col2" ....` // // Prerequisites: // - all aliased tables must be written as `tablename AS alias` (the variant without the AS keyword is invalid) // - a star only expands to the (single) table in FROM. Use *, table2.* if there exists a second (joined) table // - No weird SQL syntax, this "parser" is not very robust... // type DBPreprocessor struct { db sq.DB lock sync.Mutex cacheColumns map[string][]string cacheQuery map[string]string } var regexAlias = regexp.MustCompile("([A-Za-z_\\-0-9]+)\\s+AS\\s+([A-Za-z_\\-0-9]+)") func NewDBPreprocessor(db sq.DB) *DBPreprocessor { return &DBPreprocessor{ db: db, lock: sync.Mutex{}, cacheColumns: make(map[string][]string), cacheQuery: make(map[string]string), } } func (pp *DBPreprocessor) PrePing(ctx context.Context) error { return nil } func (pp *DBPreprocessor) PreTxBegin(ctx context.Context, txid uint16) error { return nil } func (pp *DBPreprocessor) PreTxCommit(txid uint16) error { return nil } func (pp *DBPreprocessor) PreTxRollback(txid uint16) error { return nil } func (pp *DBPreprocessor) PreQuery(ctx context.Context, txID *uint16, sql *string, params *sq.PP) error { sqlOriginal := *sql pp.lock.Lock() v, ok := pp.cacheQuery[sqlOriginal] pp.lock.Unlock() if ok { *sql = v return nil } if !strings.HasPrefix(sqlOriginal, "SELECT ") { return nil } idxFrom := strings.Index(sqlOriginal, " FROM ") if idxFrom < 0 { return nil } fromTableName := strings.Split(strings.TrimSpace(sqlOriginal[idxFrom+len(" FROM"):]), " ")[0] sels := strings.TrimSpace(sqlOriginal[len("SELECT "):idxFrom]) split := strings.Split(sels, ",") newsel := make([]string, 0) aliasMap := make(map[string]string) for _, v := range regexAlias.FindAllStringSubmatch(sqlOriginal, idxFrom+len(" FROM")) { aliasMap[strings.TrimSpace(v[2])] = strings.TrimSpace(v[1]) } for _, expr := range split { expr = strings.TrimSpace(expr) if expr == "*" { columns, err := pp.getTableColumns(ctx, fromTableName) if err != nil { return err } for _, colname := range columns { newsel = append(newsel, fmt.Sprintf("%s.%s AS \"%s\"", fromTableName, colname, colname)) } } else if strings.HasSuffix(expr, ".*") { tableName := expr[0 : len(expr)-2] if tableRealName, ok := aliasMap[tableName]; ok { columns, err := pp.getTableColumns(ctx, tableRealName) if err != nil { return err } for _, colname := range columns { newsel = append(newsel, fmt.Sprintf("%s.%s AS \"%s.%s\"", tableName, colname, tableName, colname)) } } else if tableName == fromTableName { columns, err := pp.getTableColumns(ctx, tableName) if err != nil { return err } for _, colname := range columns { newsel = append(newsel, fmt.Sprintf("%s.%s AS \"%s\"", tableName, colname, colname)) } } else { columns, err := pp.getTableColumns(ctx, tableName) if err != nil { return err } for _, colname := range columns { newsel = append(newsel, fmt.Sprintf("%s.%s AS \"%s.%s\"", tableName, colname, tableName, colname)) } } } else { return nil } } newSQL := "SELECT " + strings.Join(newsel, ", ") + sqlOriginal[idxFrom:] pp.lock.Lock() pp.cacheQuery[sqlOriginal] = newSQL pp.lock.Unlock() log.Debug().Msgf("Preprocessed SQL statement from '%s' --to--> '%s'", sqlOriginal, newSQL) *sql = newSQL return nil } func (pp *DBPreprocessor) PreExec(ctx context.Context, txID *uint16, sql *string, params *sq.PP) error { return nil } func (pp *DBPreprocessor) PostPing(result error) { // } func (pp *DBPreprocessor) PostTxBegin(txid uint16, result error) { // } func (pp *DBPreprocessor) PostTxCommit(txid uint16, result error) { // } func (pp *DBPreprocessor) PostTxRollback(txid uint16, result error) { // } func (pp *DBPreprocessor) PostQuery(txID *uint16, sqlOriginal string, sqlReal string, params sq.PP) { // } func (pp *DBPreprocessor) PostExec(txID *uint16, sqlOriginal string, sqlReal string, params sq.PP) { // } func (pp *DBPreprocessor) getTableColumns(ctx context.Context, tablename string) ([]string, error) { pp.lock.Lock() v, ok := pp.cacheColumns[tablename] pp.lock.Unlock() if ok { return v, nil } type res struct { Name string `db:"name"` } rows, err := pp.db.Query(ctx, "PRAGMA table_info('"+tablename+"');", sq.PP{}) if err != nil { return nil, err } resrows, err := sq.ScanAll[res](rows, sq.SModeFast, sq.Unsafe, true) if err != nil { return nil, err } columns := langext.ArrMap(resrows, func(v res) string { return v.Name }) if len(columns) == 0 { return nil, errors.New("no columns in table '" + tablename + "' (table does not exist?)") } pp.lock.Lock() pp.cacheColumns[tablename] = columns pp.lock.Unlock() return columns, nil }