A PostgreSQL client library written in pure Lua (MoonScript)

$ opm get GoCodeIT-Inc/pgmoon



> Note: Have you updated from an older version of OpenResty? You must update to > pgmoon 1.12 or above, due to a change in Lua pattern compatibility to avoid incorrect > results from queries that return affected rows.

pgmoon is a PostgreSQL client library written in pure Lua (MoonScript).

pgmoon was originally designed for use in [OpenResty][] to take advantage of the [cosocket api]( to provide asynchronous queries but it also works in the regular any Lua environment where [LuaSocket][] or [cqueues][] is available.

It's a perfect candidate for running your queries both inside OpenResty's environment and on the command line (eg. tests) in web frameworks like [Lapis][].


    $ luarocks install pgmoon

<details> <summary>Using <a href="">OpenResty's OPM</a></summary>

    $ opm get leafo/pgmoon



pgmoon supports a wide range of environments and libraries, so it may be necessary to install additional dependencies depending on how you intend to communicate with the database:

> Tip: If you're using OpenResty then no additional dependencies are needed > (generally, a crypto library may be necessary for some authentication > methods)

A socket implementation is required to use pgmoon, depending on the environment you can chose one:

  • [OpenResty][] — The built in socket is used, no additional dependencies necessary

  • [LuaSocket][] — luarocks install luasocket

  • [cqueues][] — luarocks install cqueues

If you're on PUC Lua 5.1 or 5.2 then you will need a bit libray (not needed for LuaJIT):

    $ luarocks install luabitop

If you want to use JSON types you will need lua-cjson

    $ luarocks install lua-cjson

SSL connections may require an additional dependency:

  • OpenResty — No additional dependencies required

  • LuaSocket — luarocks install luasec

  • cqueues — luarocks install luaossl

Password authentication may require a crypto library, [luaossl][].

    $ luarocks install luaossl

> Note: [LuaCrypto][] can be used as a fallback, but the library is abandoned and not recommended for use

> Note: Use within [OpenResty][] will prioritize built in functions if possible


    local pgmoon = require("pgmoon")
    local pg ={
      host = "",
      port = "5432",
      database = "mydb",
      user = "postgres"
    local res = assert(pg:query("select * from users where username = " ..

If you are using OpenResty you can relinquish the socket to the connection pool after you are done with it so it can be reused in future requests:



Functions in table returned by require("pgmoon"):


Creates a new Postgres object from a configuration object. All fields are optional unless otherwise stated. The newly created object will not automatically connect, you must call conect after creating the object.

Available options:

  • "database": the database name to connect to required

  • "host": the host to connect to (default: "")

  • "port": the port to connect to (default: "5432")

  • "user": the database username to authenticate (default: "postgres")

  • "password": password for authentication, may be required depending on server configuration

  • "ssl": enable ssl (default: false)

  • "ssl_verify": verify server certificate (default: nil)

  • "ssl_required": abort the connection if the server does not support SSL connections (default: nil)

  • "socket_type": the type of socket to use, one of: "nginx", "luasocket", cqueues (default: "nginx" if in nginx, "luasocket" otherwise)

  • "application_name": set the name of the connection as displayed in pg_stat_activity. (default: "pgmoon")

  • "pool": (OpenResty only) name of pool to use when using OpenResty cosocket (default: "#{host}:#{port}:#{database}")

  • "pool_size": (OpenResty only) Passed directly to OpenResty cosocket connect function, see docs

  • "backlog": (OpenResty only) Passed directly to OpenResty cosocket connect function, see docs

  • "cqueues_openssl_context": Manually created opensssl.ssl.context to use when created cqueues SSL connections

  • "luasec_opts": Manually created options object to use when using LuaSec SSL connections

Methods on the Postgres object returned by new:

success, err = postgres:connect()

Connects to the Postgres server using the credentials specified in the call to new. On success returns true, on failure returns nil and the error message.


Sets the timeout value (in milliseconds) for all subsequent socket operations (connect, write, receive). This function does not have any return values.

success, err = postgres:disconnect()

Closes the socket to the server if one is open. No other methods should be called on the object after this other than another call to connect.

success, err = postgres:keepalive(...)

Relinquishes socket to OpenResty socket pool via the setkeepalive method. Any arguments passed here are also passed to setkeepalive.

result, num_queries = postgres:query(query_string)

result, err, partial, num_queries = postgres:query(query_string)

Sends a query to the server. On failure returns nil and the error message.

On success returns a result depending on the kind of query sent.

SELECT queries, INSERT with returning, or anything else that returns a result set will return an array table of results. Each result is a hash table where the key is the name of the column and the value is the result for that row of the result.

    local res = pg:query("select id, name from users")

Might return:

        id = 123,
        name = "Leafo"
        id = 234,
        name = "Lee"

Any queries that affect rows like UPDATE, DELETE, or INSERT return a table result with the affected_rows field set to the number of rows affected.

    local res = pg:query("delete from users")

Might return:

      affected_rows = 2

Any queries with no result set or updated rows will return true.

This method also supports sending multiple queries at once by separating them with a ;. The number of queries executed is returned as a second return value after the result object. When more than one query is executed then the result object changes slightly. It becomes a array table holding all the individual results:

    local res, num_queries = pg:query([[
      select id, name from users;
      select id, title from posts

Might return:

    num_queries = 2
    res = {
          id = 123,
          name = "Leafo"
          id = 234,
          name = "Lee"
          id = 546,
          title = "My first post"

Similarly for queries that return affected rows or just true, they will be wrapped up in an addition array table when there are multiple of them. You can also mix the different query types as you see fit.

Because Postgres executes each query at a time, earlier ones may succeed and further ones may fail. If there is a failure with multiple queries then the partial result and partial number of queries executed is returned after the error message.

escaped = postgres:escape_literal(val)

Escapes a Lua value for use as a Postgres value interpolated into a query string. When sending user provided data into a query you should use this method to prevent SQL injection attacks.

escaped = postgres:escape_identifier(val)

Escapes a Lua value for use as a Postgres identifier. This includes things like table or column names. This does not include regular values, you should use escape_literal for that. Identifier escaping is required when names collide with built in language keywords.

str = tostring(postgres)

Returns string representation of current state of Postgres object.

SSL connections

pgmoon can establish an SSL connection to a Postgres server. It can also refuse to connect to it if the server does not support SSL. Just as pgmoon depends on LuaSocket for usage outside of OpenResty, it depends on luaossl/LuaSec for SSL connections in such contexts.

    local pgmoon = require("pgmoon")
    local pg ={
      host = "",
      ssl = true, -- enable SSL
      ssl_verify = true, -- verify server certificate
      ssl_required = true, -- abort if the server does not support SSL connections
      ssl_version = "tlsv1_2", -- e.g., defaults to highest available, no less than TLS v1.1 (LuaSec only)
      cafile = "...", -- certificate authority (LuaSec only)
      cert = "...", -- client certificate (LuaSec only)
      key = "...", -- client key (LuaSec only)

> Note: In Postgres 12 and above, the minium SSL version accepted by client > connections is 1.2. When using LuaSocket + LuaSec to connect to an SSL > server, if you don't specify an ssl_version then tlsv1_2 is used.

In OpenResty, make sure to configure the lua_ssl_trusted_certificate directive if you wish to verify the server certificate.

Authentication types

Postgres has a handful of authentication types. pgmoon currently supports Trust and MD5 authentication.

Type conversion

Postgres has a very rich set of types built in. pgmoon will do its best to convert any Postgres types into the appropriate Lua type.

All integer, floating point, and numeric types are converted into Lua's number type. The boolean type is converted into a Lua boolean. The JSON type is decoded into a Lua table using Lua CJSON. Lua tables can be encoded to JSON as described below.

Any array types are automatically converted to Lua array tables. If you need to encode an array in Lua to Postgres' array syntax you can use the pgmoon.arrays module. See below.

Any other types are returned as Lua strings.

Handling arrays

Arrays are automatically decoded when they are returned from a query. Numeric, string, and boolean types are automatically loaded accordingly. Nested arrays are also supported.

Use encode_array to encode a Lua table to array syntax for a query:

    local pgmoon = require("pgmoon")
    local pg =
    local encode_array = require("pgmoon.arrays").encode_array
    local my_array = {1,2,3,4,5}
    pg:query("insert into some_table (some_arr_col) values(" .. encode_array(my_array) .. ")")

Empty Arrays

When trying to encode an empty array an error will be thrown. Postgres requires a type when using an array. When there are values in the array Postgres can infer the type, but with no values in the array no type can be inferred. This is illustrated in the erorr provided by Postgres:

    postgres=# select ARRAY[];
    ERROR:  cannot determine type of empty array
    LINE 1: select ARRAY[];
    HINT:  Explicitly cast to the desired type, for example ARRAY[]::integer[].

Handling JSON

json and jsonb types are automatically decoded when they are returned from a query.

Use encode_json to encode a Lua table to the JSON syntax for a query:

    local pgmoon = require("pgmoon")
    local pg =
    local encode_json = require("pgmoon.json").encode_json
    local my_tbl = {hello = "world"}
    pg:query("insert into some_table (some_json_col) values(" .. encode_json(my_tbl) .. ")")

Handling hstore

Because hstore is an extension type, a query is reuired to find out the type id before pgmoon can automatically decode it. Call the setup_hstore method on your connection object after connecting to set it up.

    local pgmoon = require("pgmoon")
    local pg =

Use encode_hstore to encode a Lua table into hstore syntax when updating and inserting:

    local encode_hstore = require("pgmoon.hstore").encode_hstore
    local tbl = {foo = "bar"}
    pg:query("insert into some_table (hstore_col) values(" .. encode_hstore(tbl) .. ")")

You can manually decode a hstore value from string using the decode_hstore function. This is only required if you didn't call setup_hstore.

    local decode_hstore = require("pgmoon.hstore").decode_hstore
    local res = pg:query("select * from some_table")
    local hstore_tbl = decode_hstore(res[1].hstore_col)

Converting NULLs

By default NULLs in Postgres are converted to nil, meaning they aren't visible in the resulting tables. If you want to convert NULLs to some visible value set convert_null to true on the Postgres object:

    local pgmoon = require("pgmoon")
    local pg =
    pg.convert_null = true
    local res = pg:query("select NULL the_null")
    assert(pg.NULL == res[1].the_null)

As shown above, the NULL value is set to pg.NULL. You can change this value to make pgmoon use something else as NULL. For example if you're using OpenResty you might want to reuse ngx.null.


Author: Leaf Corcoran (leafo) (@moonscript) Email: Homepage: <>


  • 1.13.0 — 2021-10-13 - Add support for scram_sha_256_auth (@murillopaula), 'backlog' and 'pool_size' options while using ngx.socket (@xiaocang), update LuaSec ssl_protocol default options (@jeremymv2), application_name option (@mecampbellsoup)

  • 1.12.0 — 2021-01-06 - Lua pattern compatibility fix, Support for Lua 5.1 through 5.4 (@jprjr). Fix bug where SSL vesrion was not being passed. Default to TLS v1.2 when using LuaSec. Luabitop is no longer automatically installed as a dependency. New test suite.

  • 1.11.0 — 2020-03-26 - Allow for TLS v1.2 when using LuaSec (Miles Elam)

  • 1.10.0 — 2019-04-15 - Support luaossl for crypto functions, added better error when missing crypto library

  • 1.9.0 — 2018-04-02 - nginx pool name includes user, connection reports name as pgmoon

  • 1.8.0 — 2016-11-07 — Add cqueues support, SSL calling fix for Nginx cosocket (@thibaultCha)

  • 1.7.0 — 2016-09-21 — Add to opm, add support for openresty pool, better default pool, support for hstore (@edan)

  • 1.6.0 — 2016-07-21 — Add support for json and jsonb array decoding

  • 1.5.0 — 2016-07-12 — Add SSL support (@thibaultCha), Add UUID array type (@edan), Add support for notifications (@starius)

  • 1.4.0 — 2016-02-18 — Add support for decoding jsonb, add a json serializer (@thibaultCha)

  • 1.3.0 — 2016-02-11 — Fix bug parsing a string that looked like a number failed, add support for using in ngx when in init context (@thibaultCha), add cleartext password auth, fix warning with md5 auth

  • 1.2.0 — 2015-07-10 — Add support for PostgreSQL Arrays

  • 1.1.1 — 2014-08-12 — Fix a bug with md5 auth

  • 1.1.0 — 2014-05-21 — Add support for multiple queries in one call

  • 1.0.0 — 2014-05-19 — Initial release

License (MIT)

Copyright (C) 2021 by Leaf Corcoran

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.


[luaossl]: [LuaCrypto]: [LuaSec]: [Lapis]: [OpenResty]: [LuaSocket]: [cqueues]:


Leaf Corcoran (leafo)