node-red-contrib-postgresql

node-red-contrib-postgresql is a Node-RED node to query a PostgreSQL 🐘 database.

It supports splitting the resultset and backpressure (flow control), to allow working with large datasets.

It supports parameterized queries and multiple queries.

Outputs

The response (rows) is provided in msg.payload as an array.

An exception is if the Split results option is enabled and the Number of rows per message is set to 1, then msg.payload is not an array but the single-row response.

Additional information is provided as msg.pgsql.rowCount and msg.pgsql.command. See the underlying documentation for details.

In the case of multiple queries, then msg.pgsql is an array.

Inputs

SQL query template

This node uses the Mustache template system to generate queries based on the message:

-- INTEGER id column
SELECT * FROM table WHERE id = {{{ msg.id }}};

-- TEXT id column
SELECT * FROM table WHERE id = '{{{ msg.id }}}';

Parameterized query

Parameters for parameterized queries can be passed as a parameter array params of the msg object:

// In a function, provide parameters for the parameterized query
msg.params = [ msg.id ];

-- In this node, use a parameterized query
SELECT * FROM table WHERE id = $1;

Installation

Using the Node-RED Editor

You can install node-red-contrib-postgresql directly using the editor: Select Manage Palette from the menu (top right), and then select the Install tab in the palette.

Using npm

You can alternatively install the npm-packaged node:

Locally within your user data directory (by default, $HOME/.node-red):

cd $HOME/.node-red
npm i node-red-contrib-postgresql

or globally alongside Node-RED:

npm i -g node-red-contrib-postgresql

You will then need to restart Node-RED.

Backpressure

This node supports backpressure / flow control: when the Split results option is enabled, it waits for a tick before releasing the next batch of lines, to make sure the rest of your Node-RED flow is ready to process more data (instead of risking an out-of-memory condition), and also conveys this information upstream.

So when the Split results option is enabled, this node will only output one message at first, and then awaits a message containing a truthy msg.tick before releasing the next message.

To make this behaviour potentially automatic (avoiding manual wires), this node declares its ability by exposing a truthy node.tickConsumer for downstream nodes to detect this feature, and a truthy node.tickProvider for upstream nodes. Likewise, this node detects upstream nodes using the same back-pressure convention, and automatically sends ticks.

Example of flow

Example adding a new column in a table, then streaming (split) many lines from that table, batch-updating several lines at a time, then getting a sample consisting of a few lines:

Example: flow.json

The debug nodes illustrate some relevant information to look at.

Sequences for split results

When the Split results option is enabled (streaming), the messages contain some information following the conventions for messages sequences.

{
  payload: '...',
    parts: {
      id: 0.1234, // sequence ID, randomly generated (changes for every sequence)
      index: 5, // incremented for each message of the same sequence
      count: 6, // total number of messages; only available in the last message of a sequence
      parts: {}, // optional upstream parts information
    },
    complete: true, // True only for the last message of a sequence
}

Credits

Major rewrite in July 2021 by Alexandre Alapetite (Alexandra Institute), of parents forks: andreabat / ymedlop / HySoaKa, with inspiration from node-red-contrib-re-postgres (code).

This node builds uppon the node-postgres (pg) library.

Contributions and collaboration welcome.

tedeh/node-red-contrib-postgresql