# Handling multi-connection

Often you will need to connect to two or more database, due to legacy code.

Clear offers multi-connections possibility, and your model can live in a specific database.

If not multiple connection are set, clear use `default` connection as living place for the models.

### Setup the multiple connections

```ruby
  Clear::SQL.init("default", "postgres://[USER]:[PASSWORD]@[HOST]/[DATABASE]")
  Clear::SQL.add_connection("secondary", "postgres://[USER]:[PASSWORD]@[HOST]/[DATABASE]")
```

You can also use hash notation:

```ruby
  Clear::SQL.init(
    "default" => "postgres://[USER]:[PASSWORD]@[HOST]/[DATABASE]",
    "legacy" => "postgres://[USER]:[PASSWORD]@[HOST]/[DATABASE]"
  )
```

### Setup model connection

You can then just change the class property `connection` in your model definition:

```ruby
class OldUser
  self.table = "users"
  self.connection = "legacy"
end
```

{% hint style="info" %}
Migrations always occurs to the database under `default` connection
{% endhint %}

{% hint style="danger" %}
Models between different connections should not share relations. We cannot guarantee the behavior in case you connect models between differents databases.
{% endhint %}

### Other connection with SQL Builder

In low-level API, you can call `use_connection` to force a request to be called on a specific collection:

```ruby
Clear::SQL.select.use_connection("legacy").from("users").fetch{ |u| ... }
```


---

# 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://clear.gitbook.io/project/additional-and-advanced-features/handling-multi-connection.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.