Modified sql_server south backend to get South Migrations work with Azure SQL Backend

pyodbc.py

from datetime import date, datetime, time
from warnings import warn
from django.db import models
from django.db.models import fields
from south.db import generic
from south.db.generic import delete_column_constraints, invalidate_table_constraints, copy_column_constraints
from south.exceptions import ConstraintDropped
from south.utils.py3 import string_types
try:
    from django.utils.encoding import smart_text                    # Django >= 1.5
except ImportError:
    from django.utils.encoding import smart_unicode as smart_text   # Django < 1.5
from django.core.management.color import no_style

class DatabaseOperations(generic.DatabaseOperations):
    """
    django-pyodbc (sql_server.pyodbc) implementation of database operations.
    """
    
    backend_name = "pyodbc"
    
    add_column_string = 'ALTER TABLE %s ADD %s;'
    alter_string_set_type = 'ALTER COLUMN %(column)s %(type)s'
    alter_string_set_null = 'ALTER COLUMN %(column)s %(type)s NULL'
    alter_string_drop_null = 'ALTER COLUMN %(column)s %(type)s NOT NULL'
    
    allows_combined_alters = False

    drop_index_string = 'DROP INDEX %(index_name)s ON %(table_name)s'
    drop_constraint_string = 'ALTER TABLE %(table_name)s DROP CONSTRAINT %(constraint_name)s'
    delete_column_string = 'ALTER TABLE %s DROP COLUMN %s'

    #create_check_constraint_sql = "ALTER TABLE %(table)s " + \
    #                              generic.DatabaseOperations.add_check_constraint_fragment 
    create_foreign_key_sql = "ALTER TABLE %(table)s ADD CONSTRAINT %(constraint)s " + \
                             "FOREIGN KEY (%(column)s) REFERENCES %(target)s"
    create_unique_sql = "ALTER TABLE %(table)s ADD CONSTRAINT %(constraint)s UNIQUE (%(columns)s)"
    
    
    default_schema_name = "dbo"
    
    has_booleans = False


    @delete_column_constraints
    def delete_column(self, table_name, name):
        q_table_name, q_name = (self.quote_name(table_name), self.quote_name(name))

        # Zap the constraints
        for const in self._find_constraints_for_column(table_name,name):
            params = {'table_name':q_table_name, 'constraint_name': const}
            sql = self.drop_constraint_string % params
            self.execute(sql, [])

        # Zap the indexes
        for ind in self._find_indexes_for_column(table_name,name):
            params = {'table_name':q_table_name, 'index_name': ind}
            sql = self.drop_index_string % params
            self.execute(sql, [])

        # Zap default if exists
        drop_default = self.drop_column_default_sql(table_name, name)
        if drop_default:
            sql = "ALTER TABLE [%s] %s" % (table_name, drop_default)
            self.execute(sql, [])

        # Finally zap the column itself
        self.execute(self.delete_column_string % (q_table_name, q_name), [])

    def _find_indexes_for_column(self, table_name, name):
        "Find the indexes that apply to a column, needed when deleting"

        sql = """
            SELECT i.name -- s.name, t.name,  c.name
            FROM sys.tables t
            INNER JOIN sys.indexes i ON i.object_id = t.object_id
            INNER JOIN sys.index_columns ic ON ic.object_id = t.object_id
            INNER JOIN sys.columns c ON c.object_id = t.object_id
                                     AND ic.column_id = c.column_id
            WHERE i.is_unique=0 AND i.is_primary_key=0 AND i.is_unique_constraint=0
              AND t.name = '%s'
              AND c.name = '%s'
        """
        idx = self.execute(sql % (table_name, name), [])
        return [i[0] for i in idx]


    def _find_constraints_for_column(self, table_name, name, just_names=True):
        """
        Find the constraints that apply to a column, needed when deleting. Defaults not included.
        This is more general than the parent _constraints_affecting_columns, as on MSSQL this
        includes PK and FK constraints.
        """

        sql = """
         SELECT CC.[CONSTRAINT_NAME]
              ,TC.[CONSTRAINT_TYPE]
              ,CHK.[CHECK_CLAUSE]
              ,RFD.TABLE_SCHEMA
              ,RFD.TABLE_NAME
              ,RFD.COLUMN_NAME
              -- used for normalized names
              ,CC.TABLE_NAME
              ,CC.COLUMN_NAME
          FROM [INFORMATION_SCHEMA].[TABLE_CONSTRAINTS] TC
          JOIN INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE CC
               ON TC.CONSTRAINT_CATALOG = CC.CONSTRAINT_CATALOG 
              AND TC.CONSTRAINT_SCHEMA = CC.CONSTRAINT_SCHEMA
              AND TC.CONSTRAINT_NAME = CC.CONSTRAINT_NAME
          LEFT JOIN INFORMATION_SCHEMA.CHECK_CONSTRAINTS CHK
               ON CHK.CONSTRAINT_CATALOG = CC.CONSTRAINT_CATALOG
              AND CHK.CONSTRAINT_SCHEMA = CC.CONSTRAINT_SCHEMA
              AND CHK.CONSTRAINT_NAME = CC.CONSTRAINT_NAME
              AND 'CHECK' = TC.CONSTRAINT_TYPE
          LEFT JOIN INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS REF
               ON REF.CONSTRAINT_CATALOG = CC.CONSTRAINT_CATALOG
              AND REF.CONSTRAINT_SCHEMA = CC.CONSTRAINT_SCHEMA
              AND REF.CONSTRAINT_NAME = CC.CONSTRAINT_NAME
              AND 'FOREIGN KEY' = TC.CONSTRAINT_TYPE
          LEFT JOIN INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE RFD
               ON RFD.CONSTRAINT_CATALOG = REF.UNIQUE_CONSTRAINT_CATALOG
              AND RFD.CONSTRAINT_SCHEMA = REF.UNIQUE_CONSTRAINT_SCHEMA
              AND RFD.CONSTRAINT_NAME = REF.UNIQUE_CONSTRAINT_NAME
          WHERE CC.CONSTRAINT_CATALOG = CC.TABLE_CATALOG
            AND CC.CONSTRAINT_SCHEMA = CC.TABLE_SCHEMA
            AND CC.TABLE_CATALOG = %s
            AND CC.TABLE_SCHEMA = %s
            AND CC.TABLE_NAME = %s
            AND CC.COLUMN_NAME = %s 
        """
        db_name = self._get_setting('name')
        schema_name = self._get_schema_name()
        table = self.execute(sql, [db_name, schema_name, table_name, name])
        
        if just_names:
            return [r[0] for r in table]
        
        all = {}
        for r in table:
            cons_name, type = r[:2]
            if type=='PRIMARY KEY' or type=='UNIQUE':
                cons = all.setdefault(cons_name, (type,[]))
                sql = '''
                SELECT COLUMN_NAME
                FROM INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE RFD
                WHERE RFD.CONSTRAINT_CATALOG = %s
                  AND RFD.CONSTRAINT_SCHEMA = %s
                  AND RFD.TABLE_NAME = %s
                  AND RFD.CONSTRAINT_NAME = %s
                '''
                columns = self.execute(sql, [db_name, schema_name, table_name, cons_name])
                cons[1].extend(col for col, in columns)
            elif type=='CHECK':
                cons = (type, r[2])
            elif type=='FOREIGN KEY':
                if cons_name in all:
                    raise NotImplementedError("Multiple-column foreign keys are not supported")
                else:
                    cons = (type, r[3:6])
            else:
                raise NotImplementedError("Don't know how to handle constraints of type "+ type)
            all[cons_name] = cons
        return all

    @invalidate_table_constraints        
    def alter_column(self, table_name, name, field, explicit_name=True, ignore_constraints=False):
        """
        Alters the given column name so it will match the given field.
        Note that conversion between the two by the database must be possible.
        Will not automatically add _id by default; to have this behavour, pass
        explicit_name=False.

        @param table_name: The name of the table to add the column to
        @param name: The name of the column to alter
        @param field: The new field definition to use
        """
        self._fix_field_definition(field)

        if not ignore_constraints:
            qn = self.quote_name
            sch = qn(self._get_schema_name())
            tab = qn(table_name)
            table = ".".join([sch, tab])
            try:
                self.delete_foreign_key(table_name, name)
            except ValueError:
                # no FK constraint on this field. That's OK.
                pass
            constraints = self._find_constraints_for_column(table_name, name, False)
            for constraint in constraints.keys():
                params = dict(table_name = table,
                              constraint_name = qn(constraint))
                sql = self.drop_constraint_string % params
                self.execute(sql, [])
                
        ret_val = super(DatabaseOperations, self).alter_column(table_name, name, field, explicit_name, ignore_constraints=True)
        
        if not ignore_constraints:
            for cname, (ctype,args) in constraints.items():
                params = dict(table = table,
                              constraint = qn(cname))
                if ctype=='UNIQUE':
                    params['columns'] = ", ".join(map(qn,args))
                    sql = self.create_unique_sql % params
                elif ctype=='PRIMARY KEY':
                    params['columns'] = ", ".join(map(qn,args))
                    sql = self.create_primary_key_string % params
                elif ctype=='FOREIGN KEY':
                    continue
                    # Foreign keys taken care of below 
                    #target = "%s.%s(%s)" % tuple(map(qn,args))
                    #params.update(column = qn(name), target = target)
                    #sql = self.create_foreign_key_sql % params
                elif ctype=='CHECK':
                    warn(ConstraintDropped("CHECK "+ args, table_name, name))
                    continue
                    #TODO: Some check constraints should be restored; but not before the generic
                    #      backend restores them.
                    #params['check'] = args
                    #sql = self.create_check_constraint_sql % params
                else:
                    raise NotImplementedError("Don't know how to handle constraints of type "+ type)                    
                self.execute(sql, [])
            # Create foreign key if necessary
            if field.rel and self.supports_foreign_keys:
                self.execute(
                    self.foreign_key_sql(
                        table_name,
                        field.column,
                        field.rel.to._meta.db_table,
                        field.rel.to._meta.get_field(field.rel.field_name).column
                    )
                )
                model = self.mock_model("FakeModelForIndexCreation", table_name)
                for stmt in self._get_connection().creation.sql_indexes_for_field(model, field, no_style()):
                    self.execute(stmt)


        return ret_val
    
    def _alter_set_defaults(self, field, name, params, sqls): 
        "Subcommand of alter_column that sets default values (overrideable)"
        # First drop the current default if one exists
        table_name = self.quote_name(params['table_name'])
        drop_default = self.drop_column_default_sql(table_name, name)
        if drop_default:
            sqls.append((drop_default, []))
            
        # Next, set any default
        
        if field.has_default():
            default = field.get_default()
            literal = self._value_to_unquoted_literal(field, default)
            sqls.append(('ADD DEFAULT %s for %s' % (self._quote_string(literal), self.quote_name(name),), []))

    def _value_to_unquoted_literal(self, field, value):
        # Start with the field's own translation
        conn = self._get_connection()
        value = field.get_db_prep_save(value, connection=conn)
        # This is still a Python object -- nobody expects to need a literal.
        if isinstance(value, string_types):
            return smart_text(value)
        elif isinstance(value, (date,time,datetime)):
            return value.isoformat()
        else:
            #TODO: Anybody else needs special translations?
            return str(value) 
    def _default_value_workaround(self, value):
        if isinstance(value, (date,time,datetime)):
            return value.isoformat()
        else:
            return super(DatabaseOperations, self)._default_value_workaround(value)
        
    def _quote_string(self, s):
        return "'" + s.replace("'","''") + "'"
    

    def drop_column_default_sql(self, table_name, name, q_name=None):
        "MSSQL specific drop default, which is a pain"

        sql = """
        SELECT object_name(cdefault)
        FROM syscolumns
        WHERE id = object_id('%s')
        AND name = '%s'
        """
        cons = self.execute(sql % (table_name, name), [])
        if cons and cons[0] and cons[0][0]:
            return "DROP CONSTRAINT %s" % cons[0][0]
        return None

    def _fix_field_definition(self, field):
        if isinstance(field, (fields.BooleanField, fields.NullBooleanField)):
            if field.default == True:
                field.default = 1
            if field.default == False:
                field.default = 0

    # This is copied from South's generic add_column, with two modifications:
    # 1) The sql-server-specific call to _fix_field_definition
    # 2) Removing a default, when needed, by calling drop_default and not the more general alter_column
    @invalidate_table_constraints
    def add_column(self, table_name, name, field, keep_default=False):
        """
        Adds the column 'name' to the table 'table_name'.
        Uses the 'field' paramater, a django.db.models.fields.Field instance,
        to generate the necessary sql

        @param table_name: The name of the table to add the column to
        @param name: The name of the column to add
        @param field: The field to use
        """
        self._fix_field_definition(field)
        sql = self.column_sql(table_name, name, field)
        if sql:
            params = (
                self.quote_name(table_name),
                sql,
            )
            sql = self.add_column_string % params
            self.execute(sql)

            # Now, drop the default if we need to
            if not keep_default and field.default is not None:
                field.default = fields.NOT_PROVIDED
                #self.alter_column(table_name, name, field, explicit_name=False, ignore_constraints=True)
                self.drop_default(table_name, name, field)

    @invalidate_table_constraints
    def drop_default(self, table_name, name, field):
        fragment = self.drop_column_default_sql(table_name, name)
        if fragment:
            table_name = self.quote_name(table_name)
            sql = " ".join(["ALTER TABLE", table_name, fragment])
            self.execute(sql)        


    @invalidate_table_constraints
    def create_table(self, table_name, field_defs):
        # Tweak stuff as needed
        for _, f in field_defs:
            self._fix_field_definition(f)

        # Run
        super(DatabaseOperations, self).create_table(table_name, field_defs)

    def _find_referencing_fks(self, table_name):
        "MSSQL does not support cascading FKs when dropping tables, we need to implement."

        # FK -- Foreign Keys
        # UCTU -- Unique Constraints Table Usage
        # FKTU -- Foreign Key Table Usage
        # (last two are both really CONSTRAINT_TABLE_USAGE, different join conditions)
        sql = """
        SELECT FKTU.TABLE_SCHEMA as REFING_TABLE_SCHEMA,
               FKTU.TABLE_NAME as REFING_TABLE_NAME,
               FK.[CONSTRAINT_NAME] as FK_NAME
        FROM [INFORMATION_SCHEMA].[REFERENTIAL_CONSTRAINTS] FK
        JOIN [INFORMATION_SCHEMA].[CONSTRAINT_TABLE_USAGE] UCTU
          ON FK.UNIQUE_CONSTRAINT_CATALOG = UCTU.CONSTRAINT_CATALOG and
             FK.UNIQUE_CONSTRAINT_NAME = UCTU.CONSTRAINT_NAME and
             FK.UNIQUE_CONSTRAINT_SCHEMA = UCTU.CONSTRAINT_SCHEMA
        JOIN [INFORMATION_SCHEMA].[CONSTRAINT_TABLE_USAGE] FKTU
          ON FK.CONSTRAINT_CATALOG = FKTU.CONSTRAINT_CATALOG and
             FK.CONSTRAINT_NAME = FKTU.CONSTRAINT_NAME and
             FK.CONSTRAINT_SCHEMA = FKTU.CONSTRAINT_SCHEMA
        WHERE FK.CONSTRAINT_CATALOG = %s
          AND UCTU.TABLE_SCHEMA = %s -- REFD_TABLE_SCHEMA
          AND UCTU.TABLE_NAME = %s -- REFD_TABLE_NAME
        """
        db_name = self._get_setting('name')
        schema_name = self._get_schema_name()
        return self.execute(sql, [db_name, schema_name, table_name])
                
    @invalidate_table_constraints
    def delete_table(self, table_name, cascade=True):
        """
        Deletes the table 'table_name'.
        """
        if cascade:
            refing = self._find_referencing_fks(table_name)
            for schmea, table, constraint in refing:
                table = ".".join(map (self.quote_name, [schmea, table]))
                params = dict(table_name = table,
                              constraint_name = self.quote_name(constraint))
                sql = self.drop_constraint_string % params
                self.execute(sql, [])
            cascade = False
        super(DatabaseOperations, self).delete_table(table_name, cascade)
            
    @copy_column_constraints
    @delete_column_constraints
    def rename_column(self, table_name, old, new):
        """
        Renames the column of 'table_name' from 'old' to 'new'.
        WARNING - This isn't transactional on MSSQL!
        """
        if old == new:
            # No Operation
            return
        # Examples on the MS site show the table name not being quoted...
        params = (table_name, self.quote_name(old), self.quote_name(new))
        self.execute("EXEC sp_rename '%s.%s', %s, 'COLUMN'" % params)

    @invalidate_table_constraints
    def rename_table(self, old_table_name, table_name):
        """
        Renames the table 'old_table_name' to 'table_name'.
        WARNING - This isn't transactional on MSSQL!
        """
        if old_table_name == table_name:
            # No Operation
            return
        params = (self.quote_name(old_table_name), self.quote_name(table_name))
        self.execute('EXEC sp_rename %s, %s' % params)

    def _db_type_for_alter_column(self, field): 
        return self._db_positive_type_for_alter_column(DatabaseOperations, field)

    def _alter_add_column_mods(self, field, name, params, sqls):
        return self._alter_add_positive_check(DatabaseOperations, field, name, params, sqls)

    @invalidate_table_constraints
    def delete_foreign_key(self, table_name, column):
        super(DatabaseOperations, self).delete_foreign_key(table_name, column)
        # A FK also implies a non-unique index
        find_index_sql = """
            SELECT i.name -- s.name, t.name,  c.name
            FROM sys.tables t
            INNER JOIN sys.schemas s ON t.schema_id = s.schema_id
            INNER JOIN sys.indexes i ON i.object_id = t.object_id
            INNER JOIN sys.index_columns ic ON ic.object_id = t.object_id
            INNER JOIN sys.columns c ON c.object_id = t.object_id 
                                     AND ic.column_id = c.column_id
            WHERE i.is_unique=0 AND i.is_primary_key=0 AND i.is_unique_constraint=0
              AND s.name = %s
              AND t.name = %s
              AND c.name = %s
            """
        schema = self._get_schema_name()
        indexes = self.execute(find_index_sql, [schema, table_name, column])
        qn = self.quote_name
        for index in (i[0] for i in indexes if i[0]): # "if i[0]" added because an empty name may return
            self.execute("DROP INDEX %s on %s.%s" % (qn(index), qn(schema), qn(table_name) ))