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