title: How to define many-to-many relation with existing table with Tortoise ORM
body: <p>I have the following models (and an enum) defined:</p>
  <pre class="lang-py prettyprint-override"><code>from tortoise import models, fields
  from enum import Enum
  
  class WorkspaceUserRole(str, Enum):
      owner = &quot;owner&quot;
      collaborator = &quot;collaborator&quot;
  
  class User(models.Model):
      id = fields.UUIDField(pk=True)
  
  class Workspace(models.Model):
      id = fields.UUIDField(pk=True)
  
  class WorkspaceUser(models.Model):
      id = fields.UUIDField(pk=True)
      user = fields.ForeignKeyField(&quot;models.User&quot;, &quot;workspace_users&quot;)
      workspace = fields.ForeignKeyField(&quot;models.Workspace&quot;, &quot;workspace_users&quot;)
      role = fields.CharEnumField(WorkspaceUserRole)
  </code></pre>
  <p>I would like to do something like:</p>
  <pre class="lang-py prettyprint-override"><code>user = ... # fetch a User
  workspaces = await user.workspaces.all()
  </code></pre>
  <p>But that relation does not exist. Adding it to User obviously conflicts with the
  existing <code>workspaceuser</code> table.</p>
  <p>How do I perform this query, or add the relation to the User model?</p>