# 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](/developer-guide-agents-nodejs/data-sources/provided-data-sources/mongoose.md), 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 %}


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.forestadmin.com/developer-guide-agents-nodejs/getting-started/migrating/steps/datasource.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.