GraphPG

Tool for querying a PostgreSQL database with graphs. Lighter and faster than Hasura and PostGraphile.

Table of Contents

• Install
• Usage
• Graph
  • Anatomy
  • Arguments
  • Schemas
  • Aliases
  • Filters
  • Nesting
• Performance

Install

Use npm to install the latest version.

npm i graphpg

Usage

The graphpg function converts a graph string to an SQL SELECT statement. Learn how to write graphs in the graph section below.

import graphpg from 'graphpg'
// or
const { graphpg } = require('graphpg')

const graph = `foo { * }`

const sql = graphpg(graph)

console.log(sql)

with cte_1 as (
    select
        json_agg(to_json(foo)) as v
    from foo
)
select
    coalesce(cte_1.v, '[]') as foo
from cte_1;

Graph

Basic knowledge of GraphQL is recommended however, this specification does not follow the GraphQL specification.

Anatomy

The graph structure is similar to that of a GraphQL query, without the root-level curly braces. Graphs are made up of objects and fields. An object represents a table, while fields represent columns of a table. The top-most object is a special kind of object known as the root object, of which there can be many.

foo {                          // root
  *                            // field
}
bar {                          // root
  id                           // field
  baz(from: id, to: bar_id) {  // object
    id                         // field
    bar_id                     // field
  }
}

Arguments

Table of arguments. Optional and required arguments are marked with one ✓ and two ✓✓ checkmarks respectively.

| | Description | Default | Root | Object | Field | | ------ | ------------------ | :-----: | :--: | :----: | :---: | | Where | SQL WHERE | | ✓ | ✓ | ✓ | | Order | SQL ORDER BY | | ✓ | ✓ | | | Limit | SQL LIMIT | | ✓ | ✓ | | | Offset | SQL OFFSET | | ✓ | ✓ | | | From | Parent join column | | | ✓✓ | | | To | Nested join column | | | ✓✓ | | | Join | Join type | left | | ✓ | | | Many | Returns many rows? | true | | ✓ | | | Middle | Is junction table? | false | | ✓ | |

Schemas

To select a table from a particular database schema, write the schema and table name separated by a dot.

animal.dog {
  *
}

Aliases

To rename a key in the returned JSON object, use an alias as shown below. Here breed is an alias of the type column.

dog {
  name
  breed: type
}

Filters

To select only those records that match certain criteria, SQL WHERE, ORDER BY, LIMIT and OFFSET clauses are supported.

dog(where: "color = black", order: "age desc", limit: 10) {
  *
}

Nesting

Nesting an object is the equivalent of an SQL JOIN clause. Just like SQL JOIN clauses, nesting requires a join condition. The join condition is built using the required object arguments from and to, where from is a column in the parent object and to is a column in the nested object. In most cases these are primary and foreign key columns.

By default, tables are LEFT joined unless the join argument is specified. All PostgreSQL join types are supported.

When dealing with one-to-one or many-to-one relationships, using many: false will return a single object instead of an array of objects. In addition, when dealing with a many-to-many relationship the middle (i.e. junction) table can be omitted from the returned JSON object by specifying middle: true.

dog {
  name
  age
  owner(from: owner_id, to: id, many: false) {
    name
  }
}

Performance

The generated SQL has been carefully designed to be simple and computationally cost-effective. Query plan analysis shows our generated SQL SELECT statements have a significantly lower total cost and take less time to compute than those of Hasura and PostGraphile.