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 Lua environment as well using LuaSocket (and optionally LuaCrypto for MD5 authentication)

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

local pgmoon = require("pgmoon")
local pg = pgmoon.new({
  host = "127.0.0.1",
  port = "5432",
  database = "mydb",
  user = "postgres"
})

assert(pg:connect())

local res = assert(pg:query("select * from users where username = " ..
  pg:escape_literal("leafo")))

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

pg:keepalive()

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

Creates a new Postgres object. Does not connect automatically. Takes a table of options. The table can have the following keys:

• "host": the host to connect to (default: "127.0.0.1")
• "port": the port to connect to (default: "5432")
• "user": the database username to authenticate (default: "postgres")
• "database": the database name to connect to required
• "password": password for authentication, optional depending on server configuration

Methods on the Postgres object returned by new:

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.

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.

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

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.

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.

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.

Returns string representation of current state of Postgres object.

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

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.

Any array types are automatically converted to Lua arary 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.

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 = pgmoon.new(auth)
pg:connect()

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

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 = pgmoon.new(auth)
pg:connect()

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: [email protected]
Homepage: http://leafo.net

• 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

Copyright (C) 2014 by Leaf Corcoran

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