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)

Unix Socket

Using Unix sockets instead of TCP connection can improve performance up to 30% ~ 175% for some operations.

To use Unix sockets with db_postgres, change the server address to the socket file path:

import db_postgres ## Change "localhost" or "127.0.0.1" to the socket file path
let db = db_postgres.open("/run/postgresql", "user", "password", "database")
echo db.getAllRows(sql"SELECT version();")
db.close()

The socket file path is operating system specific and distribution specific, additional configuration may or may not be needed on your postgresql.conf. The Postgres server must be on the same computer and only works for Unix-like operating systems.

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, since

Types

DbConn = PPGconn

encapsulates a database connection Source Edit

Row = seq[string]

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

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

a handle that can be Source Edit

SqlPrepared = distinct string

a identifier for the prepared queries Source Edit

Procs

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

raises a DbError exception. Source Edit

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

DB quotes the string. Source Edit

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. Source Edit

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

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

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

executes the query and raises EDB if not successful. Source Edit

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

Source Edit

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. Source Edit

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

returns text for given column of the row Source Edit

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

Return cstring of given column of the row Source Edit

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

returns number of columns in the row Source Edit

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. Source Edit

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

Source Edit

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

executes the query and returns the whole result dataset. Source Edit

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

executes the prepared query and returns the whole result dataset. Source Edit

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. Source Edit

proc getValue(db: DbConn; stmtName: SqlPrepared; 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. Source Edit

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. Source Edit

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. Source Edit

proc tryInsert(db: DbConn; query: SqlQuery; pkName: string;
               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. Source Edit

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

executes the query (typically "INSERT") and returns the generated ID Source Edit

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. Source Edit

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

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

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

closes the database connection. Source Edit

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.

Source Edit

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

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

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

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

executes the prepared query and iterates over the result dataset. Source Edit

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. Source Edit

iterator instantRows(db: DbConn; stmtName: SqlPrepared;
                     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. Source Edit

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

Source Edit

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

same as fastRows, but slower and safe. Source Edit

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

same as fastRows, but slower and safe. Source Edit

Exports

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