# Oplog API

The JourneyApps Oplog API provides an ordered log of all create, update and delete operations that occurred on the cloud datastore for one of your JourneyApps applications. Polling the Oplog allows you to sync your own database with JourneyApps.

<table><thead><tr><th width="541">Relative URL</th><th>HTTP Request Method</th></tr></thead><tbody><tr><td><code>/api/v4/</code><em><code>backend-deployment-id</code></em><code>/oplog.json?start=</code><em><code>x</code></em></td><td>GET</td></tr><tr><td><code>/api/v4/</code><em><code>backend-deployment-id</code></em><code>/oplog.json?start=</code><em><code>x</code></em><code>&#x26;end=</code><em><code>y</code></em><code>&#x26;limit=</code><em><code>z</code></em></td><td>GET</td></tr></tbody></table>

### Parameters

`start` and `end` specify the range of sequence IDs (see below for explanation) of the Oplog to query. All entries with `start <= sequence_id < end` are returned.

`limit` is the limit of entries returned in a single API call. The default is 400, and the maximum is 1000 (subject to change).

### Response

The response will contain a list of Oplog entries no more than the limit. If there are no entries in the specified range, an empty array is returned.

Each entry contains the following info:

<table><thead><tr><th width="196">Key</th><th>Description</th></tr></thead><tbody><tr><td><code>sequence</code></td><td>Sequence ID — a strictly incrementing ID identifying the entry. Always greater than 0 and less than 2^63.</td></tr><tr><td><code>operation</code></td><td><strong>create</strong>, <strong>update</strong> or <strong>delete</strong>.</td></tr><tr><td><code>object</code></td><td>The new state of the object. The <code>updated_at</code> timestamp is the time that the write was made to the database.</td></tr></tbody></table>

The response also contains a field called `datamodel_hash`, matching the value from `datamodel.json`. This can be used to detect changes to the data model (when deployed). Note that this hash is always for the current version of the data model, even when a historical oplog range is requested. Also note that the `object` is returned according to the current data model definition, not the historical one.

### Polling

The Oplog may be polled to monitor changes to the database. Polling should be performed at most once per second. To poll, the client must keep track of the latest sequence id returned. For the next query, that sequence id + 1 should be used in the `start` parameter.

### Obtaining the most recent entries

If you need to start syncing from a certain point in time, or if you simply want to obtain an app's most recent DB operations, you can do this by appending `?tail=true` to your query. This will return the app's most recent DB operations (currently defaults to 400 operations).

### Examples

{% hint style="info" %}
**BASE-URL**

The below examples contain a `BASE-URL` placeholder. Please refer to the [HTTP Endpoints](https://docs.journeyapps.com/reference/introduction#http-endpoints) section to get the base URL relevant to your deployment.
{% endhint %}

#### Retrieve the 5 first writes to the database:

{% tabs %}
{% tab title="HTTP" %}

```http
GET BASE-URL/api/v4/533bda53027894f69b001055/oplog.json?limit=5&start=0
```

{% endtab %}

{% tab title="curl" %}

```shell
curl "BASE-URL/api/v4/533bda53027894f69b001055/oplog.json?limit=5&start=0" \
    -u "533bda53027894f69b001055:7Ajj5htRY1uzw7b4w23V"
```

{% endtab %}

{% tab title="ruby" %}

```ruby
require 'rest-client'
journey = RestClient::Resource.new "BASE-URL/api/v4", "533bda53027894f69b001055", "7Ajj5htRY1uzw7b4w23V"
journey["533bda53027894f69b001055/oplog.json"].get :params => {:start=>0, :limit=>5}
```

{% endtab %}
{% endtabs %}

Response:

{% code title="json" %}

```json
{
    "entries": [
        {
            "sequence": 6009123137931706000,
            "operation": "update",
            "events": [],
            "object": {
                "id": "42059e2e-d2a2-11e3-a9f3-001e6733fe3c",
                "type": "task",
                "updated_at": "2014-05-03T09:06:48Z",
                "name": "First Task",
                "instructions": "Update me",
                "status": null,
                "category_id": null
            }
        },
        {
            "sequence": 6112271540663878000,
            "operation": "create",
            "events": [],
            "object": {
                "id": "1e47acd2-ad0f-11e4-8513-001e6733fe3c",
                "type": "user",
                "updated_at": "2015-02-05T08:15:17Z",
                "name": "Joe Smith"
            }
        },
        {
            "sequence": 6112271738232373000,
            "operation": "update",
            "events": [],
            "object": {
                "id": "1e47acd2-ad0f-11e4-8513-001e6733fe3c",
                "type": "user",
                "updated_at": "2015-02-05T08:16:03Z",
                "name": "Bruce Wayne"
            }
        },
        {
            "sequence": 6112271772592112000,
            "operation": "create",
            "events": [],
            "object": {
                "id": "3e7e18b0-ad0f-11e4-9d6d-001e6733fe3c",
                "type": "user",
                "updated_at": "2015-02-05T08:16:11Z",
                "name": "Tony Stark"
            }
        },
        {
            "sequence": 6112271910031065000,
            "operation": "update",
            "events": [],
            "object": {
                "id": "71fafc16-ba4f-11e3-8de0-001e6733fe3c",
                "type": "category",
                "updated_at": "2015-02-05T08:16:43Z",
                "name": "Cleaning"
            }
        }
    ],
    "datamodel_hash": "d9cca721a735dac4efe709e0f3518373"
}
```

{% endcode %}

#### Retrieve the next 5 writes:

{% tabs %}
{% tab title="HTTP" %}

```http
GET BASE-URL/api/v4/533bda53027894f69b001055/oplog.json?limit=5&start=6112271910031065000
```

{% endtab %}

{% tab title="curl" %}

```shell
curl "BASE-URL/api/v4/533bda53027894f69b001055/oplog.json?limit=5&start=6112271910031065000" \
    -u "533bda53027894f69b001055:7Ajj5htRY1uzw7b4w23V"
```

{% endtab %}

{% tab title="ruby" %}

```ruby
require 'rest-client'
journey = RestClient::Resource.new "BASE-URL/api/v4", "533bda53027894f69b001055", "7Ajj5htRY1uzw7b4w23V"
journey["533bda53027894f69b001055/oplog.json"].get :params => {:start=>6112271910031065000, :limit=>5}
```

{% endtab %}
{% endtabs %}