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    Fix ChangeField failure with index+column type changes on MySQL.
    
 
    

    



 
    
 
    

  Review Request #14922
  —
  Created March 17, 2026 and updated 

 
    


    




    




    






 
    
  
    
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  david
 
    

    





    
 
 
    
  Django Evolution
 
    

    





    
 
 
    
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  django-evolution
 
    

    





    
 
 
    
  
 
    

    



 
    



    


    
 
    




  

    
 
 
    
  
    When a ChangeField mutation changes both the field type and
    
unique/db_index attributes, MySQL's MODIFY COLUMN runs before the
    
index is dropped. MySQL rejects this for TEXT or BLOB columns with
    
the error "BLOB/TEXT column used in key specification without a key
    
length".
    

    This happened because ChangeField.mutate() returns early after
    
change_column_type() when change_column_type_sets_attrs is True
    
(MySQL), skipping the change_column_attrs() call that handles index
    
drops.
    

    change_column_type() now processes db_index/unique changes from
    
new_attrs when change_column_type_sets_attrs is True, emitting
    
index drops as pre-SQL (before the MODIFY) and index adds as post-SQL
    
(after). The SQLite3 backend also calls the new helper to keep in-memory
    
database state in sync.
    
 
    

    





  

    
 
 
    
  
      

    • Ran unit tests without the fix and verified that the new tests failed with
      
  the same issue I saw in the wild.
      • 

    • Ran unit tests with the fix and verified that it was now fixed.
      • 

    • Ran dbtests for mysql, sqlite, and postgresql.
      • 

    
 
    

    




 
    

    





    
 
    




  
    
 
 
    
  


    
 
    
  
   
    

    Summary
    ID

   
    
      
  

   
    

    

     
    
      Fix ChangeField failure with index+column type changes on MySQL.
      
    When a `ChangeField` mutation changes both the field type and
`unique`/`db_index` attributes, MySQL's `MODIFY COLUMN` runs before the
index is dropped. MySQL rejects this for `TEXT` or `BLOB` columns with
the error "BLOB/TEXT column used in key specification without a key
length".

This happened because `ChangeField.mutate()` returns early after
`change_column_type()` when `change_column_type_sets_attrs` is `True`
(MySQL), skipping the `change_column_attrs()` call that handles index
drops.

`change_column_type()` now processes `db_index`/`unique` changes from
`new_attrs` when `change_column_type_sets_attrs` is `True`, emitting
index drops as pre-SQL (before the `MODIFY`) and index adds as post-SQL
(after). The SQLite3 backend also calls the new helper to keep in-memory
database state in sync.

Testing Done:
- Ran unit tests without the fix and verified that the new tests failed with
  the same issue I saw in the wild.
- Ran unit tests with the fix and verified that it was now fixed.
- Ran dbtests for mysql, sqlite, and postgresql.
    
     
    

        		
    qnonyqrrwwqqowzwqpqlwpvvslzxpvum

   
    


      
 
    

    
    
 
    

    






 





    
 
 
 
    
  
    
   
    
    
    
     
    
    
    
      
     
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david




   
    
   
    
  
    
 
    


 
    
  
    

   
    

   
    

    
    
Review request changed
    
    
    
    
     


      


     
    
    
   
    


  
    
  
    
  
    




    









  
    
   
    
    Commits:
   
    
   
    
    
    



    
 
    
  
   
    

    

    Summary
    ID

   
    
      
  

   
    

    

    

     
    
      Fix ChangeField failure with index+column type changes on MySQL.
      
    When a `ChangeField` mutation changes both the field type and
`unique`/`db_index` attributes, MySQL's `MODIFY COLUMN` runs before the
index is dropped. MySQL rejects this for `TEXT` or `BLOB` columns with
the error "BLOB/TEXT column used in key specification without a key
length".

This happened because `ChangeField.mutate()` returns early after
`change_column_type()` when `change_column_type_sets_attrs` is `True`
(MySQL), skipping the `change_column_attrs()` call that handles index
drops.

`change_column_type()` now processes `db_index`/`unique` changes from
`new_attrs` when `change_column_type_sets_attrs` is `True`, emitting
index drops as pre-SQL (before the `MODIFY`) and index adds as post-SQL
(after). The SQLite3 backend also calls the new helper to keep in-memory
database state in sync.

Testing Done:
- Ran unit tests without the fix and verified that the new tests failed with
  the same issue I saw in the wild.
- Ran unit tests with the fix and verified that it was now fixed.
- Ran dbtests for mysql, sqlite, and postgresql.
    
     
    

        		
    qnonyqrrwwqqowzwqpqlwpvvslzxpvum

   
    



   
    

    

    

     
    
      Fix ChangeField failure with index+column type changes on MySQL.
      
    When a `ChangeField` mutation changes both the field type and
`unique`/`db_index` attributes, MySQL's `MODIFY COLUMN` runs before the
index is dropped. MySQL rejects this for `TEXT` or `BLOB` columns with
the error "BLOB/TEXT column used in key specification without a key
length".

This happened because `ChangeField.mutate()` returns early after
`change_column_type()` when `change_column_type_sets_attrs` is `True`
(MySQL), skipping the `change_column_attrs()` call that handles index
drops.

`change_column_type()` now processes `db_index`/`unique` changes from
`new_attrs` when `change_column_type_sets_attrs` is `True`, emitting
index drops as pre-SQL (before the `MODIFY`) and index adds as post-SQL
(after). The SQLite3 backend also calls the new helper to keep in-memory
database state in sync.

Testing Done:
- Ran unit tests without the fix and verified that the new tests failed with
  the same issue I saw in the wild.
- Ran unit tests with the fix and verified that it was now fixed.
- Ran dbtests for mysql, sqlite, and postgresql.
    
     
    

        		
    qnonyqrrwwqqowzwqpqlwpvvslzxpvum

   
    


      
 
    

    


    

   
    
  
    




  
    
   
    
    Diff:
   
    
   
    
    
     Revision 2 (+712)
    Show changes
     
        django_evolution/db/common.py 
        django_evolution/db/sqlite3.py 
        django_evolution/tests/test_change_field.py 
        django_evolution/tests/db/mysql.py 
        django_evolution/tests/db/postgresql.py 
        django_evolution/tests/db/sqlite3.py 
     
    
   
    
  
    





    



    
 
    
  
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