# src/db_connector/db_mysql

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Note: In order to use this module, run `nimble install db_connector`.

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_connector/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_connector/db_mysql
    import std/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

mysql, db_common, dbutils

# Types

    DbConn = distinct PMySQL

  encapsulates a database connection

    InstantRow = object

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

    Row = seq[string]

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

# Procs

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

  Returns text for given column of the row.

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

  closes the database connection.

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

  raises a DbError exception.

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

  DB quotes the string. Note that this doesn't escape `%` and `_`.

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

  executes the query and raises EDB if not successful.

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

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

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

  executes the query and returns the whole result dataset.

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

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

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

  same as insertId

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

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

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

  Returns number of columns in the row.

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

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

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

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

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

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

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

  same as tryInsertID

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

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

    proc unsafeColumnAt(row: InstantRow; index: int): cstring {.inline, ...raises: [],
        tags: [], forbids: [].}

  Return cstring of given column of the row

# Iterators

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

  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; columns: var DbColumns; query: SqlQuery;
                         args: varargs[string, `$`]): InstantRow {.
        ...raises: [DbError], tags: [], forbids: [].}

  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; query: SqlQuery; args: varargs[string, `$`]): InstantRow {.
        ...tags: [ReadDbEffect], raises: [DbError], forbids: [].}

  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], forbids: [].}

  same as `fastRows`, but slower and safe.

# Exports

DbColumn, DbTypeKind, DbColumns, DbError, ReadDbEffect, SqlQuery, sql, dbError, DbEffect, DbType, WriteDbEffect