Convert data on AlterField django migration : <p>I have a production database and need to keep safe the data. I want to change a Field in model and convert all data inside that database with this change.</p>

<p>Old field</p>

<pre><code>class MyModel(models.Model):
    field_name = models.TimeField()
</code></pre>

<p>Changed field</p>

<pre><code>class MyModel(models.Model):
    field_name = models.PositiveIntegerField()
</code></pre>

<p>Basically I want to convert the TimeField value (that has a Time object) in minutes.</p>

<p>Example: I have in an object <code>time(hour=2, minute=0, second=0)</code> and I want to convert that field value in all database table to <code>120</code> when I apply the migrate.</p>
