dataloader-cache-lru/README.md

LRU (least recently used) cache for Facebook's DataLoader.

# dataloader-cache-lru

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> LRU (least recently used) cache for Facebook's DataLoader.

## Installation

```
npm install dataloader-cache-lru --save
```

## Documentation

DataLoader, by default, uses the standard Map which simply grows until the DataLoader is released.
The default is appropriate when requests to your application are short-lived.

Longer lived DataLoaders, such as ones which persist between GraphQL queries, will build up memory
pressure unless the size of the cache is controlled.
Furthermore, if records mutate, their cache entries must be removed.

This DataLoader-compatible cache implements a LRU (least recently used) cache, it deletes the
least recently used items when the cache size is exceeded.
 


## Complete Example

```js
const DataLoader = require('dataloader');
const dataLoaderCacheLru = require('dataloader-cache-lru');

const cacheMap = dataLoaderCacheLru({ max: 3 }); // see options in isaacs/node-lru-cache
const dataloader = new DataLoader(batchLoadFn, { cacheMap });

Promise.all(
  ['a', 'b', 'c', 'd', 'e'].map(key => dataloader.load(key))
)
  .then(data => {
    console.log(data); // [{ key: 'a', data: 'a' }, ..., { key: 'e', data: 'e' }]
    console.log(cacheMap.keys().sort()); // ['c', 'd', 'e']
  });

// record with key 'd' has been mutated
dataloader.clear('d');
console.log(cacheMap.keys().sort()); // ['c', 'e']

function batchLoadFn (keys) {
  return Promise.all(
    keys.map(key => ({ key, data: key }))
  );
}
```

## License

Copyright (c) 2017

Licensed under the [MIT license](LICENSE).