npm package: @lotosbin/graphql-relay-connection
Description: A GraphQL Relay connection with cursor based on id, not on number offset. Can be used for MongoDB.
Author: Joon Ho Cho
Latest version: 0.0.4

# graphql-relay-connection
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A GraphQL Relay connection with custom cursor functions.
Can be used for MongoDB, Mongoose, plain objects, scalars, or any data formats.


### Install
```
npm install --save graphql-relay-connection
```

### Usage
`mongooseConnection` is predefined for you.
For other usage, scroll down to `Custom connection` section below.
```javascript
import {
  connectionDefinitions,
  connectionArgs,
} from 'graphql-relay';

import {mongooseConnection} from 'graphql-relay-connection';

const {
  connectionFromPromisedArray,
  cursorToDocument,
} = mongooseConnection;

const UserType = new GraphQLObjectType({
  name: 'User',
  fields: () => ({
    friends: {
      type: UserConnection,
      args: connectionArgs,
      resolve: (user, args) => {
        args.first = args.first || 10;
        const doc = cursorToDocument(args.after);
        const friends = User.find({
            isFriendWith: user._id,
            _id: {$gt: doc && doc._id},
          })
          .limit(args.first + 1) // add +1 for hasNextPage
          .exec()
        return connectionFromPromisedArray(friends, args);
      },
    },
  }),
});

const {
  connectionType: UserConnection,
} = connectionDefinitions({
  nodeType: UserType,
});
```

### Custom connection
Simply provide `{
  comparableToCursor,
  cursorToComparable,
  comparator
}` to `defineConnection`.

```javascript
import defineConnection from 'graphql-relay-connection';
import {
  base64,
  unbase64,
} from './util';

const PREFIX = 'number:';

// Given a comparable value, return a string cursor.
function numberToCursor(num) {
  return base64(PREFIX + num);
}

// Given a string cursor,
// return a comparable value for the comparator function.
function cursorToNumber(cursor) {
  const num = parseInt(unbase64(cursor).substring(PREFIX.length), 10);
  return isNaN(num) ? null : num;
}

// Sort function for array.sort().
// Given two values, return an interger.
function compareNumbers(num1, num2) {
  return num1 - num2;
}

const {
  connectionFromArray,
  connectionFromPromisedArray,
} = defineConnection({
  comparableToCursor: numberToCursor,
  cursorToComparable: cursorToNumber,
  comparator: compareNumbers,
});
```

### How mongoose connection is defined
```javascript
import type {
  ConnectionCursor,
} from './connectionTypes';
import defineConnection from './defineConnection';
import {
  base64,
  unbase64,
  startsWith,
} from './util';


export type ID = string;

export type Document = {
  id: ID,
};


const PREFIX = 'mongoose:';


function documentToCursor(doc: Document): ConnectionCursor {
  return base64(PREFIX + doc.id);
}


function cursorToDocument(cursor: ConnectionCursor): ?Document {
  const unbased = unbase64(cursor);
  if (startsWith(unbased, PREFIX)) {
    const id = unbased.substring(PREFIX.length);
    if (id) return {id};
  }
  return null;
}


function compareDocuments(doc1: Document, doc2: Document): number {
  if (doc1.id < doc2.id) {
    return -1;
  }
  if (doc1.id > doc2.id) {
    return 1;
  }
  return 0;
}


const {
  connectionFromArray,
  connectionFromPromisedArray,
} = defineConnection({
  comparableToCursor: documentToCursor,
  cursorToComparable: cursorToDocument,
  comparator: compareDocuments,
});


export {
  compareDocuments,
  connectionFromArray,
  connectionFromPromisedArray,
  cursorToDocument,
  documentToCursor,
};
```


### License
```
The MIT License (MIT)

Copyright (c) 2016 Joon Ho Cho

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
```