Module db_mysql

A higher level mySQL database wrapper. The same interface is implemented for other databases too.

See also: db_odbc, db_sqlite, db_postgres.

Parameter substitution

All db_* modules support the same form of parameter substitution. That is, using the ? (question mark) to signify the place where a value should be placed. For example:

sql"INSERT INTO myTable (colA, colB, colC) VALUES (?, ?, ?)"

Examples

Opening a connection to a database

import db_mysql
let db = open("localhost", "user", "password", "dbname")
db.close()

Creating a table

db.exec(sql"DROP TABLE IF EXISTS myTable")
db.exec(sql("""CREATE TABLE myTable (
                 id integer,
                 name varchar(50) not null)"""))

Inserting data

db.exec(sql"INSERT INTO myTable (id, name) VALUES (0, ?)",
        "Dominik")

Larger example

import db_mysql, math

let theDb = open("localhost", "nim", "nim", "test")

theDb.exec(sql"Drop table if exists myTestTbl")
theDb.exec(sql("create table myTestTbl (" &
    " Id    INT(11)     NOT NULL AUTO_INCREMENT PRIMARY KEY, " &
    " Name  VARCHAR(50) NOT NULL, " &
    " i     INT(11), " &
    " f     DECIMAL(18,10))"))

theDb.exec(sql"START TRANSACTION")
for i in 1..1000:
  theDb.exec(sql"INSERT INTO myTestTbl (name,i,f) VALUES (?,?,?)",
        "Item#" & $i, i, sqrt(i.float))
theDb.exec(sql"COMMIT")

for x in theDb.fastRows(sql"select * from myTestTbl"):
  echo x

let id = theDb.tryInsertId(sql"INSERT INTO myTestTbl (name,i,f) VALUES (?,?,?)",
        "Item#1001", 1001, sqrt(1001.0))
echo "Inserted item: ", theDb.getValue(sql"SELECT name FROM myTestTbl WHERE id=?", id)

theDb.close()

Imports

strutils, mysql, db_common

Types

DbConn = PMySQL

encapsulates a database connection

Row = seq[string]

a row of a dataset. NULL database values will be converted to nil.

InstantRow = object
  row: cstringArray
  len: int

a handle that can be used to get a row's column text on demand

Procs

proc dbError(db: DbConn) {.noreturn, raises: [DbError], tags: [].}

raises a DbError exception.

proc dbQuote(s: string): string {.raises: [], tags: [].}

DB quotes the string.

proc tryExec(db: DbConn; query: SqlQuery; args: varargs[string, `$`]): bool {.
    tags: [ReadDbEffect, WriteDbEffect], raises: [].}

tries to execute the query and returns true if successful, false otherwise.

proc exec(db: DbConn; query: SqlQuery; args: varargs[string, `$`]) {.
    tags: [ReadDbEffect, WriteDbEffect], raises: [DbError].}

executes the query and raises EDB if not successful.

proc `[]`(row: InstantRow; col: int): string {.inline, raises: [], tags: [].}

Returns text for given column of the row.

proc len(row: InstantRow): int {.inline, raises: [], tags: [].}

Returns number of columns in the row.

proc getRow(db: DbConn; query: SqlQuery; args: varargs[string, `$`]): Row {.
    tags: [ReadDbEffect], raises: [DbError].}

Retrieves a single row. If the query doesn't return any rows, this proc will return a Row with empty strings for each column.

proc getAllRows(db: DbConn; query: SqlQuery; args: varargs[string, `$`]): seq[Row] {.
    tags: [ReadDbEffect], raises: [DbError].}

executes the query and returns the whole result dataset.

proc getValue(db: DbConn; query: SqlQuery; args: varargs[string, `$`]): string {.
    tags: [ReadDbEffect], raises: [DbError].}

executes the query and returns the first column of the first row of the result dataset. Returns "" if the dataset contains no rows or the database value is NULL.

proc tryInsertId(db: DbConn; query: SqlQuery; args: varargs[string, `$`]): int64 {.
    tags: [WriteDbEffect], raises: [].}

executes the query (typically "INSERT") and returns the generated ID for the row or -1 in case of an error.

proc insertId(db: DbConn; query: SqlQuery; args: varargs[string, `$`]): int64 {.
    tags: [WriteDbEffect], raises: [DbError].}

executes the query (typically "INSERT") and returns the generated ID for the row.

proc execAffectedRows(db: DbConn; query: SqlQuery; args: varargs[string, `$`]): int64 {.
    tags: [ReadDbEffect, WriteDbEffect], raises: [DbError].}

runs the query (typically "UPDATE") and returns the number of affected rows

proc close(db: DbConn) {.tags: [DbEffect], raises: [].}

closes the database connection.

proc open(connection, user, password, database: string): DbConn {.tags: [DbEffect],
    raises: [DbError].}

opens a database connection. Raises EDb if the connection could not be established.

proc setEncoding(connection: DbConn; encoding: string): bool {.tags: [DbEffect],
    raises: [].}

sets the encoding of a database connection, returns true for success, false for failure.

Iterators

iterator fastRows(db: DbConn; query: SqlQuery; args: varargs[string, `$`]): Row {.
    tags: [ReadDbEffect], raises: [DbError].}

executes the query and iterates over the result dataset.

This is very fast, but potentially dangerous. Use this iterator only if you require ALL the rows.

Breaking the fastRows() iterator during a loop will cause the next database query to raise an [EDb] exception Commands out of sync.

iterator instantRows(db: DbConn; query: SqlQuery; args: varargs[string, `$`]): InstantRow {.
    tags: [ReadDbEffect], raises: [DbError].}

Same as fastRows but returns a handle that can be used to get column text on demand using []. Returned handle is valid only within the iterator body.

iterator instantRows(db: DbConn; columns: var DbColumns; query: SqlQuery;
                    args: varargs[string, `$`]): InstantRow {.raises: [DbError],
    tags: [].}

Same as fastRows but returns a handle that can be used to get column text on demand using []. Returned handle is valid only within the iterator body.

iterator rows(db: DbConn; query: SqlQuery; args: varargs[string, `$`]): Row {.
    tags: [ReadDbEffect], raises: [DbError].}

same as fastRows, but slower and safe.