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https://github.com/graphile-contrib/postgraphile-plugin-derived-field
Add derived fields in PostGraphile
https://github.com/graphile-contrib/postgraphile-plugin-derived-field
Last synced: 12 days ago
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Add derived fields in PostGraphile
- Host: GitHub
- URL: https://github.com/graphile-contrib/postgraphile-plugin-derived-field
- Owner: graphile-contrib
- License: mit
- Created: 2018-03-16T09:56:45.000Z (over 6 years ago)
- Default Branch: master
- Last Pushed: 2023-01-06T01:52:26.000Z (almost 2 years ago)
- Last Synced: 2024-10-14T11:44:18.985Z (30 days ago)
- Language: JavaScript
- Size: 1.13 MB
- Stars: 29
- Watchers: 3
- Forks: 6
- Open Issues: 6
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
[](https://www.npmjs.com/package/postgraphile-plugin-derived-field) [](https://circleci.com/gh/graphile-contrib/postgraphile-plugin-derived-field)
# postgraphile-plugin-derived-field
This plugin provides an interface for adding derived fields to the schema generated by PostGraphile v4.
The term "derived fields" is used to differentiate this approach from the standard [Computed Columns](https://www.graphile.org/postgraphile/computed-columns/) support in PostGraphile. This plugin effectively adds "computed columns in JavaScript" to your toolbelt.
## Getting Started
Define your derived fields in the `derivedFieldDefinitions` property of `graphileBuildOptions`:
``` js
const express = require("express");
const { postgraphile } = require("postgraphile");
const PostGraphileDerivedFieldPlugin = require("postgraphile-plugin-derived-field");
const app = express();
app.use(
postgraphile(pgConfig, schema, {
graphiql: true,
appendPlugins: [PostGraphileDerivedFieldPlugin],
graphileBuildOptions: {
derivedFieldDefinitions: [
// your definitions here
]
}
})
);
app.listen(5000);
```
Provide `derivedFieldDefinitions` as an array of objects with the following structure:
```
{
identifiers: Array,
inflect: function,
resolve: function,
type?: string | build => T,
description?: string
}
```
The Scenarios section below provides guidance on structuring `identifiers`, `inflect`, and `resolve` for your specific use case.
Use `type` to specify the GraphQL type that the `resolve` function returns. This can be a string identifying the GraphQL type name, or a function (with the `build` helper available as the first argument) that returns a GraphQL type. Default: String
Use `description` to populate the field description in the schema.
## Scenarios
### Derive a new field from one database column
``` js
{
identifiers: [
{
table: "my_schema.my_table",
columns: ["my_column"],
},
],
inflect: fieldName => `derivedFrom${fieldName}`,
resolve: val => `Value derived from ${val}`,
}
```
### Derive a new field from multiple database columns
``` js
{
identifiers: [
{
table: "my_schema.my_table",
columns: ["my_column", "my_other_column"],
},
],
inflect: (...fieldNames) =>
`derivedFrom${fieldNames.map(upperFirst).join("And")}`,
resolve: (my_column, my_other_column) =>
`Value derived from ${my_column} and ${my_other_column}`,
}
```
### Derive a new field from columns that have a specific tag
This approach uses the "smart comments" feature of PostGraphile to match columns that have been assigned a specific tag.
``` js
{
identifiers: [
{
tag: "mytag",
},
],
inflect: fieldName => `derivedFrom${fieldName}`,
resolve: val => `Value derived from ${val}`,
}
```
## Alternative syntax
Column names can be provided as a string: `"my_schema.my_table.my_column"`. This syntax does not support generating a derived field from multiple database columns.
Tag names can be provided as a string: `"@mytag"`
## Examples
Generate pre-signed URLs for client-side S3 GET requests
``` js
const express = require("express");
const { postgraphile } = require("postgraphile");
const PostGraphileDerivedFieldPlugin = require("postgraphile-plugin-derived-field");
const AWS = require("aws-sdk");
const s3 = new AWS.S3();
const bucket = "postgraphile-plugin-test";
const app = express();
app.use(
postgraphile(pgConfig, schema, {
graphiql: true,
appendPlugins: [PostGraphileDerivedFieldPlugin],
graphileBuildOptions: {
derivedFieldDefinitions: [
{
identifiers: ["my_schema.my_table.my_column"],
inflect: fieldName => `${fieldName}SignedUrl`,
resolve: val => s3.getSignedUrl('getObject', {Bucket: bucket, Key: val, Expires: 900})
}
]
}
})
);
app.listen(5000);
```