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- """Database functions that do comparisons or type conversions."""
- from django.db.models import Func
-
-
- class Cast(Func):
- """Coerce an expression to a new field type."""
- function = 'CAST'
- template = '%(function)s(%(expressions)s AS %(db_type)s)'
-
- def __init__(self, expression, output_field):
- super().__init__(expression, output_field=output_field)
-
- def as_sql(self, compiler, connection, **extra_context):
- extra_context['db_type'] = self.output_field.cast_db_type(connection)
- return super().as_sql(compiler, connection, **extra_context)
-
- def as_mysql(self, compiler, connection):
- # MySQL doesn't support explicit cast to float.
- template = '(%(expressions)s + 0.0)' if self.output_field.get_internal_type() == 'FloatField' else None
- return self.as_sql(compiler, connection, template=template)
-
- def as_postgresql(self, compiler, connection):
- # CAST would be valid too, but the :: shortcut syntax is more readable.
- # 'expressions' is wrapped in parentheses in case it's a complex
- # expression.
- return self.as_sql(compiler, connection, template='(%(expressions)s)::%(db_type)s')
-
-
- class Coalesce(Func):
- """Return, from left to right, the first non-null expression."""
- function = 'COALESCE'
-
- def __init__(self, *expressions, **extra):
- if len(expressions) < 2:
- raise ValueError('Coalesce must take at least two expressions')
- super().__init__(*expressions, **extra)
-
- def as_oracle(self, compiler, connection):
- # Oracle prohibits mixing TextField (NCLOB) and CharField (NVARCHAR2),
- # so convert all fields to NCLOB when that type is expected.
- if self.output_field.get_internal_type() == 'TextField':
- class ToNCLOB(Func):
- function = 'TO_NCLOB'
-
- expressions = [
- ToNCLOB(expression) for expression in self.get_source_expressions()
- ]
- clone = self.copy()
- clone.set_source_expressions(expressions)
- return super(Coalesce, clone).as_sql(compiler, connection)
- return self.as_sql(compiler, connection)
-
-
- class Greatest(Func):
- """
- Return the maximum expression.
-
- If any expression is null the return value is database-specific:
- On PostgreSQL, the maximum not-null expression is returned.
- On MySQL, Oracle, and SQLite, if any expression is null, null is returned.
- """
- function = 'GREATEST'
-
- def __init__(self, *expressions, **extra):
- if len(expressions) < 2:
- raise ValueError('Greatest must take at least two expressions')
- super().__init__(*expressions, **extra)
-
- def as_sqlite(self, compiler, connection):
- """Use the MAX function on SQLite."""
- return super().as_sqlite(compiler, connection, function='MAX')
-
-
- class Least(Func):
- """
- Return the minimum expression.
-
- If any expression is null the return value is database-specific:
- On PostgreSQL, return the minimum not-null expression.
- On MySQL, Oracle, and SQLite, if any expression is null, return null.
- """
- function = 'LEAST'
-
- def __init__(self, *expressions, **extra):
- if len(expressions) < 2:
- raise ValueError('Least must take at least two expressions')
- super().__init__(*expressions, **extra)
-
- def as_sqlite(self, compiler, connection):
- """Use the MIN function on SQLite."""
- return super().as_sqlite(compiler, connection, function='MIN')
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