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# Relay Library for GraphQL Python
GraphQL-relay-py is the [Relay] library for
[GraphQL-core].
It allows the easy creation of Relay-compliant servers using GraphQL-core.
GraphQL-Relay-Py is a Python port of
[graphql-relay-js],
while GraphQL-Core is a Python port of
[GraphQL.js],
the reference implementation of GraphQL for JavaScript.
Since version 3, GraphQL-Relay-Py and GraphQL-Core support Python 3.6 and
above only.
For older versions of Python, you can use version 2 of these libraries.
[PyPI version]
![Test Status]
![Lint Status]
[Dependency Updates]
[Python 3 Status]
[Code Style]
## Getting Started
A basic understanding of GraphQL and of the GraphQL Python implementation
is needed
to provide context for this library.
An overview of GraphQL in general is available in the
[README] for the
[Specification for GraphQL].
This library is designed to work with the
the [GraphQL-Core]
Python reference implementation of a GraphQL server.
An overview of the functionality that a Relay-compliant GraphQL server
should provide
is in the [GraphQL Relay Specification]
on the [Relay website].
That overview describes a simple set of examples that exist
as [tests] in this repository.
A good way to get started with this repository is to walk through that
documentation
and the corresponding tests in this library together.
## Using Relay Library for GraphQL Python (graphql-core)
Install Relay Library for GraphQL Python
```sh
pip install graphql-core
pip install graphql-relay
```
When building a schema for [GraphQL],
the provided library functions can be used to simplify the creation of
Relay patterns.
All the functions that are explained in the following sections must be
imported from the top level of the `graphql_relay` package, like this:
`python
from graphql_relay import connection_definitions
`
### Connections
Helper functions are provided for both building the GraphQL types
for connections and for implementing the `resolve` method for fields
returning those types.
- `connection_args` returns the arguments that fields should provide when
they return a connection type that supports bidirectional pagination.
- `forward_connection_args` returns the arguments that fields should
provide when
they return a connection type that only supports forward pagination.
- `backward_connection_args` returns the arguments that fields should
provide when
they return a connection type that only supports backward pagination.
- `connection_definitions` returns a `connection_type` and its associated
`edgeType`, given a name and a node type.
- `connection_from_array` is a helper method that takes an array and the
arguments from `connection_args`, does pagination and filtering, and
returns
an object in the shape expected by a `connection_type`'s `resolve`
function.
- `cursor_for_object_in_connection` is a helper method that takes an array
and a
member object, and returns a cursor for use in the mutation payload.
- `offset_to_cursor` takes the index of a member object in an array
and returns an opaque cursor for use in the mutation payload.
- `cursor_to_offset` takes an opaque cursor (created with
`offset_to_cursor`)
and returns the corresponding array index.
An example usage of these methods from the [test schema]:
```python
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