Rails creates database Indexes

Take the classic customer-order as an Example

1. directly create an index when creating a data table

Check the migration file of order. rails automatically adds the index for us:

2. Manually attach an index

In this case, the data table is created as a foreign key created by a common field.

To create an index, You need to manually create a migration to add the index:

Modify the migration file and manually add the index

3. Add an index to the "to-be" relationship.

Taking man-address as an example, directly creating an intermediate table does not automatically add indexes. Therefore, you need to manually add indexes to the intermediate table:

4. Suggestions

It is best to add indexes for all foreign keys.