# Configure database connection

{% hint style="success" %}
This is the official documentation of the `@forestadmin/agent` Node.js agent.
{% endhint %}

### Migrating from `forest-express-sequelize`

When using the onboarding wizard, you connected to your database using the `@forestadmin/datasource-sql` connector. To ease the migration, we recommend switching to the `@forestadmin/datasource-sequelize` connector.

Start by changing the dependency in your agent

```console
$ npm install @forestadmin/datasource-sequelize sequelize
```

Then you will need to copy your `Sequelize` models to the new project and change the `index` file.

```javascript
const { createAgent } = require('@forestadmin/agent');
const { createSequelizeDataSource } = require('@forestadmin/datasource-sequelize');
const sequelizeInstance = require('./sequelize-instance');

// Create agent and import collections from sequelize
const agent = createAgent(options).addDataSource(
  createSequelizeDataSource(sequelizeInstance),
);
```

### Migrating from `forest-express-mongoose`

#### Connect to the database

Connecting to a MongoDB instance is very similar: using the `mongoose` ODM is required. We officially support `mongoose >= 6.0`, but customers have reported working installations with `5.x`.

You will need to:

* Install the `@forestadmin/datasource-mongoose` package.
* Copy your `mongoose` models to the new project.
* Create a new `mongoose` connection to the same database as the old one.

```javascript
const { createAgent } = require('@forestadmin/agent');
const { createMongooseDataSource } = require('@forestadmin/datasource-mongoose');
const connection = require('./mongoose-connection');

// Create agent and import collections from mongoose.connection
const agent = createAgent(options).addDataSource(
  createMongooseDataSource(connection),
);
```

#### Replicate your legacy agent flattener configuration

If you are using the `forest-express-mongoose` agent, you probably are using the [flattener](https://docs.forestadmin.com/documentation/extra-help/setup/flatten-nested-fields-mongodb) feature.

In the new agent, the flattener is [more capable](https://docs.forestadmin.com/developer-guide-agents-nodejs/data-sources/provided-data-sources/mongoose), but the behavior of the new `auto` mode is different.

To replicate the behavior of the old agent, you will need to use the `manual` mode and configure the flattener manually.

{% hint style="info" %}
You may have noticed that a `flattenMode: 'legacy'` option is available. This option **does not** replicate the behavior of legacy agents, but the behavior of a previous version of the model flattener in the new agents.

If you are migrating from a legacy agent, use the `manual` mode.
{% endhint %}

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

```javascript
import { collection } from 'forest-express-mongoose';

collection('users', {
  /** ... other options ... */
  fieldsToFlatten: [
    // Flatten the contactDetails field
    'contactDetails',

    // Flatten the characteristics field, but only the first level
    { field: 'characteristics', level: 1 },
  ],
});
```

{% endtab %}

{% tab title="After" %}
If you were using `fieldsToFlatten` in your old agent.

```javascript
const agent = createAgent(options).addDataSource(
  createMongooseDataSource(connection, {
    flattenMode: 'manual',
    flattenOptions: {
      users: {
        asFields: [
          // Flatten the contactDetails field
          'contactDetails',

          // Flatten the characteristics field, but only the first level
          { field: 'characteristics', level: 1 },
        ],
      },
    },
  }),
);
```

Otherwise

```javascript
const agent = createAgent(options).addDataSource(
  createMongooseDataSource(connection, { flattenMode: 'none' }),
);
```

{% endtab %}
{% endtabs %}