Module db_postgres

A higher level PostgreSQL database wrapper. This interface is implemented for other databases also.

See also: db_odbc, db_sqlite, db_mysql.

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 (?, ?, ?)"

Note: There are two approaches to parameter substitution support by this module.

1. SqlQuery using ?, ?, ?, ... (same as all the db_* modules)

2. SqlPrepared using $1, $2, $3, ...

prepare(db, "myExampleInsert",
        sql"""INSERT INTO myTable
              (colA, colB, colC)
              VALUES ($1, $2, $3)""",
        3)

Examples

Opening a connection to a database

import db_postgres
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")

Imports

strutils, postgres, db_common

Types

DbConn = PPGconn

encapsulates a database connection

Row = seq[string]

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

InstantRow = object
  res: PPGresult               ## used to get a row's
  line: int                    ## column text on demand

a handle that can be

SqlPrepared = distinct string

a identifier for the prepared queries

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: [DbError].}

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

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

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 exec(db: DbConn; stmtName: SqlPrepared; args: varargs[string]) {.
    tags: [ReadDbEffect, WriteDbEffect], raises: [Exception, DbError].}

proc prepare(db: DbConn; stmtName: string; query: SqlQuery; nParams: int): SqlPrepared {.
    raises: [DbError], tags: [].}

Creates a new SqlPrepared statement. Parameter substitution is done via $1, $2, $3, etc.

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 getRow(db: DbConn; stmtName: SqlPrepared; args: varargs[string, `$`]): Row {.
    tags: [ReadDbEffect], raises: [Exception, DbError].}

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

executes the prepared 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 getValue(db: DbConn; stmtName: SqlPrepared; args: varargs[string, `$`]): string {.
    tags: [ReadDbEffect], raises: [Exception, 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: [DbError, ValueError].}

executes the query (typically "INSERT") and returns the generated ID for the row or -1 in case of an error. For Postgre this adds RETURNING id to the query, so it only works if your primary key is named id.

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

executes the query (typically "INSERT") and returns the generated ID for the row. For Postgre this adds RETURNING id to the query, so it only works if your primary key is named id.

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

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

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

executes 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.

Clients can also use Postgres keyword/value connection strings to connect.

Example:

con = open("", "", "", "host=localhost port=5432 dbname=mydb")

See http://www.postgresql.org/docs/current/static/libpq-connect.html#LIBPQ-CONNSTRING for more information.

Note that the connection parameter is not used but exists to maintain the nim db api.

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 potenially dangerous: If the for-loop-body executes another query, the results can be undefined. For Postgres it is safe though.

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

executes the prepared query and iterates over the result dataset.

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 iterator body.

iterator instantRows(db: DbConn; stmtName: SqlPrepared; args: varargs[string, `$`]): InstantRow {.
    tags: [ReadDbEffect], raises: [Exception, 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 iterator body.

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

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

same as fastRows, but slower and safe.

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

same as fastRows, but slower and safe.