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

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 Source
Row = seq[string]: a row of a dataset. NULL database values will be converted to nil. Source
InstantRow = tuple[res: PPGresult, line: int32]: a handle that can be used to get a row's column text on demand Source
SqlPrepared = distinct string: a identifier for the prepared queries Source

Procs

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

raises a DbError exception. Source

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

DB quotes the string. Source

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

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. Source

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

executes the query and raises EDB if not successful. Source

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

Source

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

proc `[]`(row: InstantRow; col: int32): string {.inline, raises: [], tags: [].}

returns text for given column of the row Source

proc len(row: InstantRow): int32 {.inline, raises: [], tags: [].}

returns number of columns in the row Source

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

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

Source

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

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. Source

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

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. Source

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

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

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

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. Source

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

closes the database connection. Source

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.

Source

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

Iterators

iterator fastRows(db: DbConn; query: SqlQuery; args: varargs[string, `$`]): Row {. tags: [ReadDbEffect], raises: [DbError].}: executes the query and iterates over the result dataset. This is very fast, but potenially dangerous: If the for-loop-body executes another query, the results can be undefined. For Postgres it is safe though. Source
iterator fastRows(db: DbConn; stmtName: SqlPrepared; args: varargs[string, `$`]): Row {. tags: [ReadDbEffect], raises: [Exception, DbError].}: executes the prepared query and iterates over the result dataset. Source
iterator instantRows(db: DbConn; query: SqlQuery; args: varargs[string, `$`]): InstantRow {. tags: [ReadDbEffect], raises: [DbError].}: same as fastRows but returns a handle that can be used to get column text on demand using []. Returned handle is valid only within iterator body. Source
iterator instantRows(db: DbConn; stmtName: SqlPrepared; args: varargs[string, `$`]): 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. Source
iterator rows(db: DbConn; query: SqlQuery; args: varargs[string, `$`]): Row {. tags: [ReadDbEffect], raises: [DbError].}: same as fastRows, but slower and safe. Source
iterator rows(db: DbConn; stmtName: SqlPrepared; args: varargs[string, `$`]): Row {. tags: [ReadDbEffect], raises: [Exception, DbError].}: same as fastRows, but slower and safe. Source

Module db_postgres