fix index name

[Abdeldjalil-H]

Use index_name from class Index to get index name instead of BaseSchemaGenerator._generate_index_name.

Motivation and Context

This allows you to create your custom index class that inherits from Index and override index_name method to set index name.

How Has This Been Tested?

On existing tests.

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have added the changelog accordingly.
• [x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[coveralls]

Pull Request Test Coverage Report for Build 9135160308

Details

• 1 of 3 (33.33%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.01%) to 87.945%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tortoise/indexes.py	1	3	33.33%
<!--	Total:	1	3	33.33%	-->

Totals
Change from base Build 9080530396:	0.01%
Covered Lines:	5786
Relevant Lines:	6483

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💛 - Coveralls

[abondar]

Is there reason why defining name for Index class doesn't work for you?

[Abdeldjalil-H]

In my case I am using a custom index class:

from tortoise.indexes import Index

class MyCustomIndex(Index):
    PREFIX = "idx"
    def index_name(self, schema_generator: BaseSchemaGenerator, model: models.Model):
        if self.name:
            return self.name

        table_name = model._meta.db_table

        return f"{self.PREFIX}_{table_name}_{'_'.join(self.fields)}".lower()[:64]

Then I wrap all my indexes with this custom class so the name is generated automatically. But when I run the migrations, I still get the old name.

By the way, this is not the case if you pass expressions instead of fields as you can see in the previous code.