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.
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
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 — luarocks install lua-resty-openssl
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
Parsing complex types like Arrays and HStore requires lpeg to be installed.
Example
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 status = 'active' limit 20")
assert(pg:query("update users set name = $1 where id = $2", "leafo", 99))
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:
pg:keepalive()
Considerations
PostgreSQL allows for results to use the same field name multiple times.
Because results are extracted into Lua tables, repeated fields will be
overwritten and previous values will be unavailable:
pg:query("select 1 as dog, 'hello' as dog") --> { { dog = "hello" } }
There is currently no way around this limitation. If this is something you need
then open an issue.
Reference
Functions in table returned by require("pgmoon"):
new(options={})
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: "127.0.0.1")
"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:
postgres:connect()
local 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.
postgres:settimeout(time)
postgres:settimeout(5000) -- 5 second timeout
Sets the timeout value (in milliseconds) for all subsequent socket operations
(connect, write, receive). This function does not have any return values.
The default timeout depends on the underslying socket implementation but
generally corresponds to no timeout.
postgres:disconnect()
local success, err = postgres:disconnect()
Closes the socket. Returns nil if the socket couldn't be closed. On most
socket types, connect can be called again to reestaablish a connection with
the same postgres object instance.
postgres:keepalive(...)
postgres:keepalive()
Relinquishes socket to OpenResty socket pool via the setkeepalive method. Any
arguments passed here are also passed to setkeepalive. After calling this
method, the socket is no longer available for queries and should be considered
disconnected.
Note: This method only works within OpenResty using the nginx cosocket API
postgres:query(query_string, ...)
-- return values for successful querylocal result, err, num_queries = postgres:query("select name from users limit 2")
-- return value for failure (status is nil)local status, err, partial_result, num_queries = postgres:query("select created_at from tags; select throw_error() from users")
Sends a query (or multiple queries) to the server. On failure the first return
value is nil, followed by a string describing the error. Since a single call
to postgres:query can contain multiple queries, the results of any queries that
succeeded before the error occurred are returned after the error message.
(Note: queries are atomic, they either succeed or fail. The partial result will
only contain succeed queries, not partially data from the failed query)
Additional return values: notifications and notices
In addition to the return values above, pgmoon will also return two additional
values if the query generates them, notifications an notices.
local result, err, num_queries, notifications, notices = postgres:query("drop table if exists some_table")
In this example, if the table some_table does not exist, then notices will
be an array containing a message that the table didn't exist.
The query function has two modes of operation which correspond to the two
protocols the Postgres server provides for sending queries to the database
server:
Simple protocol: you only pass in a single argument, the query string
Extended protocol: you pass in a query with parameter placeholders ($1, $2, etc.) and then pass in additional arguments which will be used as values for the placeholders
On success, the result returned depends 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.
When using the simple protocol (calling the function with a single string),
you can send 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.
postgres:escape_literal(val)
local sql_fragment = postgres:escape_literal(val)
local res = postgres:query("select created_at from users where id = ".. sql_fragment)
Escapes a Lua value int a valid SQL fragment that can be safely concatenated
into a query string. Never concatenate a variable into query without
escaping it in some way, or you may open yourself up to SQL injection
attacks.
This function is aware of the following Lua value types:
val == pgmoon.NULL → escape_literal(pgmoon.NULL) --> NULL
Any other type will throw a hard error, to ensure that you provide a value
that is safe for escaping.
postgres:escape_identifier(val)
local sql_fragment = postgres:escape_identifier(some_table_name)`
local res = postgres:query("select * from ".. sql_fragment .." limit 20)
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.
Extended and simple query protocols
pgmoon will issue your query to the database server using either the simple or
extended protocol depending if you provide parameters and parameter
placeholders in your query. The simple protocol is used for when your query is
just a string, and the extended protocol is used when you provide addition
parameters as arguments to the query method.
The protocols have some trade-offs and differences:
Extended protocol
local res, err = postgres:query("select name from users where id = $1 and status = $2", 12, "ready")
Advantage: Parameters can be included in query without risk of SQL injection attacks, no need to escape values and interpolate strings
Advantage: Supports the pgmoon_serialize method to allow for custom types to be automatically serialized into parameters for the query
Disadvantage: Only a single query can be sent a time
Disadvantage: Substantially more overhead per query. A no-op query may be 50% to 100% slower. (note that this overhead may be negligible depending on the runtime of the query itself)
Disadvantage: Some kinds of query syntax are not compatible with parameters (eg. where id in (...), dynamic expressions), so you may still need to use string interpolation and assume the associated risks
Simple protocol
local res, err = postgres:query("select name from users where id = ".. postgres:escape_literal(12) .." and status = ".. postgres:escape_literal("ready"))
Advantage: Higher performance. Low overhead per query means more queries can be sent per second, even when manually escaping and interpolating parameters
Advantage: Multiple queries can be sent in a single request (separated by ;)
Disadvantage: Any parameters to the query must be manually escaped and interpolated into the query string. This can be error prone and introduce SQL injection attacks if not done correctly
Note: The extended protocol also supports binary encoding of parameter values
& results, but since Lua treats binary as strings, it's generally going to be
faster to just consume the string values from Postgres rather than using the
binary protocol which will require binary to string conversion within Lua.
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 = pgmoon.new({
host ="127.0.0.1",
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
cafile ="...", -- certificate authority (LuaSec only)
cert ="...", -- client certificate
key ="...", -- client key
})
assert(pg:connect())
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, peer and password authentication with scram-sha-256-auth or md5.
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 deserialized into a Lua object 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_arraylocal my_array = {1,2,3,4,5}
pg:query("insert into some_table (some_arr_col) values("..encode_array(my_array) ..")")
Arrays that are returned from queries have their metatable configured for the
PostgresArray type (defined in require("pgmoon.arrays")).
Extended protocol
When using the extended query protocol (query with parameters), an array object
created with PostgresArray will automatically be serialized when passed as a
parameter.
local PostgresArray =require("pgmoon.arrays").PostgresArray
postgres:query("update user set tags = $1 where id = 44", PostgresArray({1,2,4}))
Keep in mind that calling PostgresArray mutate the argument by setting its
metatable. Make a copy first if you don't want the original object to be
mutated.
Additionally, array types must contain values of only the same type. No
run-time checking is performed on the object you pass. The type OID is
determined from the first entry of the 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[].
You can work around this error by always including a typecast with any value
you use, to allow you to pass in an empty array and continue to work with an
array of values assuming the types match.
local empty_tags = {}
pg:query("update posts set tags = "..encode_array(empty_tags) .."::text[]")
Handling JSON
json and jsonb values are automatically decoded as Lua tables in a query
result (using the cjson library if available).
To send JSON in a query you must first convert it into a string literal, then
interpolate it into your query. Ensure that you treat it like any other
paramter, and call escape_literal on the string to make it suitable to be
safely parsed as a value to PostgreSQL.
local pgmoon =require("pgmoon")
local pg = pgmoon.new(auth)
assert(pg:connect())
local my_tbl = { hello ="world" }
local json =require"cjson"
pg:query("update my_table set data = ".. db.escape_literal(json.encode(my_tbl)) .." where id = 124"
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 = pgmoon.new(auth)
pg:connect()
pg:setup_hstore()
Use encode_hstore to encode a Lua table into hstore syntax suitable for
interpolating into a query.
Note: The result of encode_hstore is a valid Postgres SQL fragment, it is
not necessary to call escape_literal on it. It can safely be inserted
directly into the query
local encode_hstore =require("pgmoon.hstore").encode_hstorelocal 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_hstorelocal res = pg:query("select * from some_table")
local hstore_tbl =decode_hstore(res[1].hstore_col)
Custom type deserializer
PostgreSQL has a rich set of types. When reading a query's results pgmoon must
attempt to interpret the types from postgres and map them to something usable
in Lua. By default implementations are included for primitives like numbers,
booleans, strings, and JSON.
You can provie you own type deserializer if you want to add custom behavior for
certain types of values returned by PostgreSQL.
You must have some knowledge of types and type OIDs. Every type in PostgreSQL
is stored in the pg_type catalog table. Each type has an OID (stored as a 32
bit positive integer) to uniquely identify it. The core types provided by
Postgres have fixed type OIDs (for example, boolean is always 16), but
third-party types may be added without fixed OIDs.
Also note that any composite versions of existing types have their own OID, for
example, while a single boolean value has type OID 16, an array of boolean
values has type OID 1000. Arrays are homogeneous and must contain the same type
for every value.
Adding support for a new type in pgmoon can be done using the
set_type_deserializer(oid, type_name, [deserializer]) method:
local pgmoon =require("pgmoon")
local pg = pgmoon.new(config)
-- in this example we create a new deserializer called bignumber and provide-- the function to deserialize (type OID 20 is an 8 byte integer)
pg:set_type_deserializer(20, "bignumber", function(val)
return"HUGENUMBER:".. val
end)
-- in this example we point another OID to the "bignumber" deserializer we-- provided above (type OID 701 is a 8 byte floating point number)
pg:set_type_deserializer(701, "bignumber")
The arguments are as follows:
oid The OID from pg_type that will be handled
name The local name of the type. This is a name that points to an existing deserializer or will be used to register a new one if the deserializer argument is
deserializer A function that takes the raw string value from Postgres and converts it into something more useful (optional). Any existing deserializer function with the same name will be overwritten
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