> For the complete documentation index, see [llms.txt](https://www.serverless-cqrs.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://www.serverless-cqrs.com/components/memory-adapter.md).

# memory-adapter

A library that implements the [Write Model](/advanced/repository/write-model.md) and [Read Model](/advanced/repository/read-model.md) Adapter interface for storing events and projections in memory. Useful for development and testing but not for production, obviously 😛.

## Methods

### build

`build({ entityName }, { eventStore, projectionStore )` 

builds a read-model and write-model adapter

#### Parameters

| attribute         | type     | description                                                                                                                                        |
| ----------------- | -------- | -------------------------------------------------------------------------------------------------------------------------------------------------- |
| `entityName`      | `string` | the name of the entity                                                                                                                             |
| `eventStore`      | `object` | (optional) an object where keys are `entityNames` and values are arrays of [commit](/advanced/repository/write-model.md#commit) objects            |
| `projectionStore` | `object` | (optional) an object where keys are entity names and values are [projections](/advanced/repository/read-model.md#projection) objects keyed by `id` |

#### Returns

an object with [write model methods](/advanced/repository/write-model.md#methods) and [read model methods](/advanced/repository/read-model.md#methods)

## Example

{% code title="adapter.js" %}

```javascript
const memoryAdapterBuilder = require('serverless-cqrs.memory-adapter')
module.exports = memoryAdapterBuilder.build({ 
  entityName: 'todo'
})
```

{% endcode %}

You can also provide the initial `eventStore` and/or `projectionStore` objects (both are optional). This is useful when writing tests.

{% code title="test.js" %}

```javascript
const { test } = require('tap')
const { build } = require('serverless-cqrs.memory-adapter')

test('loadEvents', async assert => {
  const eventStore = {
    'foo': [
      { entityId: '123', version: 0, events: [ 'a' ] },
      { entityId: '123', version: 1, events: [ 'b', 'c' ]},
      { entityId: '123', version: 3, events: [ 'd', 'e', 'f' ] },
      { entityId: '123', version: 6, events: [ 'g', 'h', 'i' ] },
    ]
  }
  const expected = [ 'd', 'e', 'f', 'g', 'h', 'i' ]

  const adapter = build({ entityName: 'foo' }, { eventStore })
  
  const res = await adapter.loadEvents('123', 1)

  assert.deepEquals(res, expected, 'returns events after given version')
})

test('get', async assert => {
  const projectionStore = {
    foo: {
      '123':{
        id: '123',
        version: 0,
        state: 'foobar',
      }
    }
  }

  const expected = {
    id: '123',
    version: 0,
    state: 'foobar',
  }

  const adapter = build({ entityName: 'foo' }, { projectionStore })
 
  const res = await adapter.get('123')

  assert.deepEquals(res, expected, 'returns exisiting projection from store')
})
```

{% endcode %}