A battle-tested PostgreSQL client with strict types, detail logging and assertions.
Slonik began as a collection of utilities designed for working with node-postgres. We continue to use node-postgres as it provides a robust foundation for interacting with PostgreSQL. However, what once was a collection of utilities has since grown into a framework that abstracts repeating code patterns, protects against unsafe connection handling and value interpolation, and provides rich debugging experience.
Slonik has been battle-tested with large data volumes and queries ranging from simple CRUD operations to data-warehousing needs.
The name of the elephant depicted in the official PostgreSQL logo is Slonik. The name itself is derived from the Russian word for "little elephant".
Read: The History of Slonik, the PostgreSQL Elephant Logo
Among the primary reasons for developing Slonik, was the motivation to reduce the repeating code patterns and add a level of type safety. This is primarily achieved through the methods such as one, many, etc. But what is the issue? It is best illustrated with an example.
Suppose the requirement is to write a method that retrieves a resource ID given values defining (what we assume to be) a unique constraint. If we did not have the aforementioned convenience methods available, then it would need to be written as:
// @flow
import {
sql
} from 'slonik';
import type {
DatabaseConnectionType
} from 'slonik';
opaque type DatabaseRecordIdType = number;
const getFooIdByBar = async (connection: DatabaseConnectionType, bar: string): Promise<DatabaseRecordIdType> => {
const fooResult = await connection.query(sql`
SELECT id
FROM foo
WHERE bar = ${bar}
`);
if (fooResult.rowCount === 0) {
throw new Error('Resource not found.');
}
if (fooResult.rowCount > 1) {
throw new Error('Data integrity constraint violation.');
}
return fooResult[0].id;
};
oneFirst method abstracts all of the above logic into:
const getFooIdByBar = (connection: DatabaseConnectionType, bar: string): Promise<DatabaseRecordIdType> => {
return connection.oneFirst(sql`
SELECT id
FROM foo
WHERE bar = ${bar}
`);
};
oneFirst throws:
NotFoundError if query returns no rowsDataIntegrityError if query returns multiple rowsDataIntegrityError if query returns multiple columnsThis becomes particularly important when writing routines where multiple queries depend on the previous result. Using methods with inbuilt assertions ensure that in case of an error, the error points to the original source of the problem. In contrast, unless assertions for all possible outcomes are typed out as in the previous example, the unexpected result of the query will be fed to the next operation. If you are lucky, the next operation will simply break; if you are unlucky, you are risking data corruption and hard to locate bugs.
Furthermore, using methods that guarantee the shape of the results, allows us to leverage static type checking and catch some of the errors even before they executing the code, e.g.
const fooId = await connection.many(sql`
SELECT id
FROM foo
WHERE bar = ${bar}
`);
await connection.query(sql`
DELETE FROM baz
WHERE foo_id = ${fooId}
`);
The above example will throw an error as the fooId is guaranteed to be an array and last query binding is expecting a primitive value.
Use createPool to create a connection pool, e.g.
import {
createPool
} from 'slonik';
const pool = createPool('postgres://');
Instance of Slonik connection pool can be then used to create a new connection, e.g.
pool.connect(async (connection) => {
await connection.query(sql`SELECT 1`);
});
The connection will be kept alive until the promise resolves (the result of the method supplied to connect()).
Refer to query method documentation to learn about the connection methods.
If you do not require having a persistent connection to the same backend, then you can directly use pool to run queries, e.g.
pool.query(sql`SELECT 1`);
Beware that in the latter example, the connection picked to execute the query is a random connection from the connection pool, i.e. using the latter method (without explicit connect()) does not guarantee that multiple queries will refer to the same backend.
createPool(
connectionConfiguration: DatabaseConfigurationType,
clientConfiguration: ClientConfigurationType
): DatabasePoolType;
type DatabaseConnectionUriType = string;
type DatabaseConfigurationType =
DatabaseConnectionUriType |
{|
+database?: string,
+host?: string,
+idleTimeoutMillis?: number,
+max?: number,
+password?: string,
+port?: number,
+user?: string
|};
/**
* @property interceptors An array of [Slonik interceptors](https://github.com/gajus/slonik#slonik-interceptors).
*/
type ClientConfigurationType = {|
+interceptors?: $ReadOnlyArray<InterceptorType>
|};
Example:
import {
createPool
} from 'slonik';
const pool = createPool('postgres://localhost');
await pool.query(sql`SELECT 1`);
Slonik only allows to check out a connection for the duration of the promise routine supplied to the pool#connect() method.
import {
createPool
} from 'slonik';
const pool = createPool('postgres://localhost');
const result = await pool.connect(async (connection) => {
await connection.query(sql`SELECT 1`);
await connection.query(sql`SELECT 2`);
return 'foo';
});
result;
// 'foo'
Connection is released back to the pool after the promise produced by the function supplied to connect() method is either resolved or rejected.
The primary reason for implementing only this connection pooling method is because the alternative is inherently unsafe, e.g.
// Note: This example is using unsupported API.
const main = async () => {
const connection = await pool.connect();
await connection.query(sql`SELECT produce_error()`);
await connection.release();
};
In this example, the error causes early rejection of the promise and a hanging connection. A fix to the above is to ensure that connection#release() is always called, i.e.
// Note: This example is using unsupported API.
const main = async () => {
const connection = await pool.connect();
let lastExecutionResult;
try {
lastExecutionResult = await connection.query(sql`SELECT produce_error()`);
} finally {
await connection.release();
}
return lastExecutionResult;
};
Slonik abstracts the latter pattern into pool#connect() method.
Functionality can be added to Slonik client by adding interceptors (middleware).
Interceptors are configured using client configuration, e.g.
import {
createPool
} from 'slonik';
const interceptors = [];
const connection = createPool('postgres://', {
interceptors
});
Interceptors are executed in the order they are added.
Interceptors implement methods that are used to change the behaviour of the database client at different stages of the connection life-cycle:
type InterceptorType = {|
+afterPoolConnection?: (connection: DatabasePoolConnectionType) => MaybePromiseType<void>,
+afterQueryExecution?: (
queryExecutionContext: QueryExecutionContextType,
query: QueryType,
result: QueryResultType<QueryResultRowType>
) => MaybePromiseType<QueryResultType<QueryResultRowType>>,
+beforePoolConnectionRelease?: (connection: DatabasePoolConnectionType) => MaybePromiseType<void>,
+beforeQueryExecution?: (
queryExecutionContext: QueryExecutionContextType,
query: QueryType
) => MaybePromiseType<QueryResultType<QueryResultRowType>> | MaybePromiseType<void>,
+transformQuery?: (
queryExecutionContext: QueryExecutionContextType,
query: QueryType
) => MaybePromiseType<QueryType>
|};
afterPoolConnectionExecuted after a connection is acquired from the connection pool (or a new connection is created), e.g.
const pool = createPool('postgres://');
// Interceptor is executed here. ↓
pool.connect();
afterQueryExecutionafterQueryExecution must return the result of the query, which will be passed down to the client.
Use afterQuery to modify the query result.
beforeQueryExecutionThis function can optionally return a direct result of the query which will cause the actual query never to be executed.
beforePoolConnectionReleaseExecuted before connection is released back to the connection pool, e.g.
const pool = await createPool('postgres://');
pool.connect(async () => {
await 1;
// Interceptor is executed here. ↓
});
transformQueryExecuted before beforeQueryExecution.
Transforms query.
createFormatFieldNameInterceptor creates an interceptor that formats query result field names.
This interceptor removes the necessity to alias field names, e.g.
connection.any(sql`
SELECT
id,
full_name "fullName"
FROM person
`);
Field name formatter uses afterQuery interceptor to format field names.
/**
* @property format The only supported format is CAMEL_CASE.
* @property test Tests whether the field should be formatted. The default behaviour is to include all fields that match ^[a-z0-9_]+$ regex.
*/
type ConfigurationType = {|
+format: 'CAMEL_CASE',
+test: (field: FieldType) => boolean
|};
(configuration: ConfigurationType) => InterceptorType;
import {
createFieldNameTransformationInterceptor,
createPool
} from 'slonik';
const interceptors = [
createFieldNameTransformationInterceptor({
format: 'CAMEL_CASE'
})
];
const connection = createPool('postgres://', {
interceptors
});
connection.any(sql`
SELECT
id,
full_name
FROM person
`);
// [
// {
// id: 1,
// fullName: 1
// }
// ]
Normalizes the query.
/**
* @property stripComments Strips comments from the query (default: true).
*/
type ConfigurationType = {|
+stripComments?: boolean
|};
(configuration?: ConfigurationType) => InterceptorType;
auto_explainexecutionTime log property describes how long it took for the client to execute the query, i.e. it includes the overhead of waiting for a connection and the network latency, among other things. However, it is possible to get the real query execution time by using auto_explain module.
There are several pre-requisites:
-- Load the extension.
LOAD 'auto_explain';
-- or (if you are using AWS RDS):
LOAD '$libdir/plugins/auto_explain';
-- Enable logging of all queries.
SET auto_explain.log_analyze=true;
SET auto_explain.log_format=json;
SET auto_explain.log_min_duration=0;
SET auto_explain.log_timing=true;
-- Enables Slonik to capture auto_explain logs.
SET client_min_messages=log;
This can be configured using afterPoolConnection interceptor, e.g.
const pool = await createPool('postgres://localhost', {
interceptors: [
{
afterPoolConnection: async (connection) => {
await connection.query(sql`LOAD 'auto_explain'`);
await connection.query(sql`SET auto_explain.log_analyze=true`);
await connection.query(sql`SET auto_explain.log_format=json`);
await connection.query(sql`SET auto_explain.log_min_duration=0`);
await connection.query(sql`SET auto_explain.log_timing=true`);
await connection.query(sql`SET client_min_messages=log`);
}
}
]
});
Slonik recognises and parses the auto_explain JSON message; Roarr logger will produce a pretty-print of the explain output, e.g.
[2018-12-31T21:15:21.010Z] INFO (30) (@slonik): notice message
notice:
level: notice
message:
Query Text: SELECT count(*) FROM actor
Plan:
Node Type: Aggregate
Strategy: Plain
Partial Mode: Simple
Parallel Aware: false
Startup Cost: 4051.33
Total Cost: 4051.34
Plan Rows: 1
Plan Width: 8
Actual Startup Time: 26.791
Actual Total Time: 26.791
Actual Rows: 1
Actual Loops: 1
Plans:
-
Node Type: Seq Scan
Parent Relationship: Outer
Parallel Aware: false
Relation Name: actor
Alias: actor
Startup Cost: 0
Total Cost: 3561.86
Plan Rows: 195786
Plan Width: 0
Actual Startup Time: 0.132
Actual Total Time: 15.29
Actual Rows: 195786
Actual Loops: 1
sql.raw to generate dynamic queriessql.raw can be used to generate fragments of an arbitrary SQL that are interpolated into the main query, e.g.
const uniquePairs = [
['a', 1],
['b', 2]
];
let placeholderIndex = 1;
const whereConditionSql = uniquePairs
.map(() => {
return needleColumns
.map((column) => {
return column + ' = $' + placeholderIndex++;
})
.join(' AND ');
})
.join(' OR ');
const values = [];
for (const pairValues of uniquePairs) {
values.push(...pairValues);
}
const query = sql`
SELECT
id
FROM foo
WHERE
${sql.raw(whereConditionSql, values)}
`;
await connection.any(query);
In the above example, query is:
{
sql: 'SELECT id FROM foo WHERE (a = $1 AND b = $2) OR (a = $3 AND b = $4)',
values: [
'a',
1,
'b',
2
]
}
Multiple sql.raw fragments can be used to create a query.
Slonik will strip all comments and line-breaks from a query before processing it.
This makes logging of the queries easier.
The implication is that your query cannot contain values that include a newline character, e.g.
// Do not do this
connection.query(sql`INSERT INTO foo (bar) VALUES ('\n')`);
If you want to communicate a value that includes a multiline character, use value placeholder interpolation, e.g.
connection.query(sql`INSERT INTO foo (bar) VALUES (${'\n'})`);
Slonik query methods can only be executed using sql tagged template literal, e.g.
import {
sql
} from 'slonik'
connection.query(sql`
SELECT 1
FROM foo
WHERE bar = ${'baz'}
`);
The above is equivalent to evaluating:
SELECT 1
FROM foo
WHERE bar = $1
query with 'baz' value binding.
sql.valueList(values: $ReadOnlyArray<PrimitiveValueExpressionType>) => ValueListSqlTokenType;
Creates a list of values, e.g.
await connection.query(sql`
SELECT (${sql.valueList([1, 2, 3])})
`);
Produces:
{
sql: 'SELECT ($1, $2, $3)',
values: [
1,
2,
3
]
}
sql.tuple(values: $ReadOnlyArray<PrimitiveValueExpressionType>) => TupleSqlTokenType;
Creates a tuple (typed row construct), e.g.
await connection.query(sql`
INSERT INTO (foo, bar, baz)
VALUES ${sql.tuple([1, 2, 3])}
`);
Produces:
{
sql: 'INSERT INTO (foo, bar, baz) VALUES ($1, $2, $3)',
values: [
1,
2,
3
]
}
sql.tupleList(tuples: $ReadOnlyArray<$ReadOnlyArray<PrimitiveValueExpressionType>>) => TupleListSqlTokenType;
Creates a list of tuples (typed row constructs), e.g.
await connection.query(sql`
INSERT INTO (foo, bar, baz)
VALUES ${sql.tupleList([
[1, 2, 3],
[4, 5, 6]
])}
`);
Produces:
{
sql: 'INSERT INTO (foo, bar, baz) VALUES ($1, $2, $3), ($4, $5, $6)',
values: [
1,
2,
3,
4,
5,
6
]
}
sql.unnestList/**
* @param aliasNames When alias names for the unnset members are not provided, then incremental names are used (a, b, c...).
*/
(
tuples: $ReadOnlyArray<$ReadOnlyArray<PrimitiveValueExpressionType>>,
columnTypes: $ReadOnlyArray<string>,
aliasNames?: $ReadOnlyArray<string>
): UnnestListSqlTokenType;
Creates a list of unnset expressions, e.g.
await connection.query(sql`
SELECT ${sql.unnestList(
[
[1, 'foo'],
[2, 'bar']
],
[
'integer',
'text'
]
)}
`);
Produces:
{
sql: 'SELECT UNNEST($1::integer[]), UNNEST($2::text[])',
values: [
[
1,
2
],
[
'foo',
'bar'
]
]
}
sql.identifier(names: $ReadOnlyArray<string>) => IdentifierTokenType;
Delimited identifiers are created by enclosing an arbitrary sequence of characters in double-quotes ("). To create create a delimited identifier, create an sql tag function placeholder value using sql.identifier, e.g.
sql`
SELECT 1
FROM ${sql.identifier(['bar', 'baz'])}
`;
Produces:
{
sql: 'SELECT 1 FROM "bar"."bar"',
values: []
}
sql.raw(rawSql: string, values?: $ReadOnlyArray<PrimitiveValueExpressionType>) => RawSqlTokenType;
Raw/ dynamic SQL can be inlined using sql.raw, e.g.
sql`
SELECT 1
FROM ${sql.raw('"bar"')}
`;
Produces:
{
sql: 'SELECT 1 FROM "bar"',
values: []
}
The second parameter of the sql.raw can be used to bind values, e.g.
sql`
SELECT ${sql.raw('$1', [1])}
`;
Produces:
{
sql: 'SELECT $1',
values: [
1
]
}
anyReturns result rows.
Example:
const rows = await connection.any(sql`SELECT foo`);
#any is similar to #query except that it returns rows without fields information.
anyFirstReturns value of the first column of every row in the result set.
DataIntegrityError if query returns multiple rows.Example:
const fooValues = await connection.anyFirst(sql`SELECT foo`);
insertUsed when inserting 1 row.
Example:
const {
insertId
} = await connection.insert(sql`INSERT INTO foo SET bar='baz'`);
The reason for using this method over #query is to leverage the strict types. #insert method result type is InsertResultType.
manyReturns result rows.
NotFoundError if query returns no rows.Example:
const rows = await connection.many(sql`SELECT foo`);
manyFirstReturns value of the first column of every row in the result set.
NotFoundError if query returns no rows.DataIntegrityError if query returns multiple rows.Example:
const fooValues = await connection.many(sql`SELECT foo`);
maybeOneSelects the first row from the result.
null if row is not found.DataIntegrityError if query returns multiple rows.Example:
const row = await connection.maybeOne(sql`SELECT foo`);
// row.foo is the result of the `foo` column value of the first row.
maybeOneFirstReturns value of the first column from the first row.
null if row is not found.DataIntegrityError if query returns multiple rows.DataIntegrityError if query returns multiple columns.Example:
const foo = await connection.maybeOneFirst(sql`SELECT foo`);
// foo is the result of the `foo` column value of the first row.
oneSelects the first row from the result.
NotFoundError if query returns no rows.DataIntegrityError if query returns multiple rows.Example:
const row = await connection.one(sql`SELECT foo`);
// row.foo is the result of the `foo` column value of the first row.
Note:
I've been asked "What makes this different from knex.js
knex('foo').limit(1)?".knex('foo').limit(1)simply generates "SELECT * FROM foo LIMIT 1" query.knexis a query builder; it does not assert the value of the result. Slonik#oneadds assertions about the result of the query.
oneFirstReturns value of the first column from the first row.
NotFoundError if query returns no rows.DataIntegrityError if query returns multiple rows.DataIntegrityError if query returns multiple columns.Example:
const foo = await connection.oneFirst(sql`SELECT foo`);
// foo is the result of the `foo` column value of the first row.
queryAPI and the result shape are equivalent to pg#query.
transactiontransaction method is used wrap execution of queries in START TRANSACTION and COMMIT or ROLLBACK. COMMIT is called if the transaction handler returns a promise that resolves; ROLLBACK is called otherwise.
transaction method can be used together with createPool method. When used to create a transaction from an instance of a pool, a new connection is allocated for the duration of the transaction.
const result = await connection.transaction(async (transactionConnection) => {
await transactionConnection.query(sql`INSERT INTO foo (bar) VALUES ('baz')`);
await transactionConnection.query(sql`INSERT INTO qux (quux) VALUES ('quuz')`);
return 'FOO';
});
result === 'FOO';
All Slonik errors extend from SlonikError, i.e. You can catch Slonik specific errors using the following logic.
import {
SlonikError
} from 'slonik';
try {
await query();
} catch (error) {
if (error instanceof SlonikError) {
// This error is thrown by Slonik.
}
}
NotFoundErrorTo handle the case where query returns less than one row, catch NotFoundError error.
import {
NotFoundError
} from 'slonik';
let row;
try {
row = await connection.one(sql`SELECT foo`);
} catch (error) {
if (!(error instanceof NotFoundError)) {
throw error;
}
}
if (row) {
// row.foo is the result of the `foo` column value of the first row.
}
DataIntegrityErrorTo handle the case where the data result does not match the expectations, catch DataIntegrityError error.
import {
NotFoundError
} from 'slonik';
let row;
try {
row = await connection.one(sql`SELECT foo`);
} catch (error) {
if (error instanceof DataIntegrityError) {
console.error('There is more than one row matching the select criteria.');
} else {
throw error;
}
}
NotNullIntegrityConstraintViolationErrorNotNullIntegrityConstraintViolationError is thrown when Postgres responds with unique_violation (23502) error.
ForeignKeyIntegrityConstraintViolationErrorForeignKeyIntegrityConstraintViolationError is thrown when Postgres responds with unique_violation (23503) error.
UniqueIntegrityConstraintViolationErrorUniqueIntegrityConstraintViolationError is thrown when Postgres responds with unique_violation (23505) error.
CheckIntegrityConstraintViolationErrorCheckIntegrityConstraintViolationError is thrown when Postgres responds with unique_violation (23514) error.
This package is using Flow types.
Refer to ./src/types.js.
The public interface exports the following types:
DatabaseConnectionTypeDatabasePoolConnectionTypeDatabaseSingleConnectionTypeUse these types to annotate connection instance in your code base, e.g.
// @flow
import type {
DatabaseConnectionType
} from 'slonik';
export default async (
connection: DatabaseConnectionType,
code: string
): Promise<number> => {
const countryId = await connection.oneFirst(sql`
SELECT id
FROM country
WHERE code = ${code}
`);
return countryId;
};
Slonik uses roarr to log queries.
To enable logging, define ROARR_LOG=true environment variable.
By default, Slonik logs the input query, query execution time and affected row count.
You can enable additional logging details by configuring the following environment variables.
# Logs query parameter values
export SLONIK_LOG_VALUES=true
SLONIK_LOG_STACK_TRACE=1 will create a stack trace before invoking the query and include the stack trace in the logs, e.g.
{"context":{"package":"slonik","namespace":"slonik","logLevel":20,"executionTime":"357 ms","queryId":"01CV2V5S4H57KCYFFBS0BJ8K7E","rowCount":1,"sql":"SELECT schedule_cinema_data_task();","stackTrace":["/Users/gajus/Documents/dev/applaudience/data-management-program/node_modules/slonik/dist:162:28","/Users/gajus/Documents/dev/applaudience/data-management-program/node_modules/slonik/dist:314:12","/Users/gajus/Documents/dev/applaudience/data-management-program/node_modules/slonik/dist:361:20","/Users/gajus/Documents/dev/applaudience/data-management-program/node_modules/slonik/dist/utilities:17:13","/Users/gajus/Documents/dev/applaudience/data-management-program/src/bin/commands/do-cinema-data-tasks.js:59:21","/Users/gajus/Documents/dev/applaudience/data-management-program/src/bin/commands/do-cinema-data-tasks.js:590:45","internal/process/next_tick.js:68:7"],"values":[]},"message":"query","sequence":4,"time":1540915127833,"version":"1.0.0"}
{"context":{"package":"slonik","namespace":"slonik","logLevel":20,"executionTime":"66 ms","queryId":"01CV2V5SGS0WHJX4GJN09Z3MTB","rowCount":1,"sql":"SELECT cinema_id \"cinemaId\", target_data \"targetData\" FROM cinema_data_task WHERE id = ?","stackTrace":["/Users/gajus/Documents/dev/applaudience/data-management-program/node_modules/slonik/dist:162:28","/Users/gajus/Documents/dev/applaudience/data-management-program/node_modules/slonik/dist:285:12","/Users/gajus/Documents/dev/applaudience/data-management-program/node_modules/slonik/dist/utilities:17:13","/Users/gajus/Documents/dev/applaudience/data-management-program/src/bin/commands/do-cinema-data-tasks.js:603:26","internal/process/next_tick.js:68:7"],"values":[17953947]},"message":"query","sequence":5,"time":1540915127902,"version":"1.0.0"}
Use @roarr/cli to pretty-print the output.
Using Atom IDE you can leverage the language-babel package in combination with the language-sql to enable highlighting of the SQL strings in the codebase.
To enable highlighting, you need to:
language-babel and language-sql packages.language-babel "JavaScript Tagged Template Literal Grammar Extensions" setting to use language-sql to highlight template literals with sql tag (configuration value: sql:source.sql).sql helper to construct the queries.For more information, refer to the JavaScript Tagged Template Literal Grammar Extensions documentation of language-babel package.
FAQs
A Node.js PostgreSQL client with strict types, detailed logging and assertions.
The npm package slonik receives a total of 70,150 weekly downloads. As such, slonik popularity was classified as popular.
We found that slonik demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 0 open source maintainers collaborating on the project.
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