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using System.Data.Linq.Mapping;
namespace System.Data.Linq.SqlClient {
/// <summary>
/// Locate cases in which there is a 'Bit' but a 'Predicate' is expected or vice-versa.
/// Transform these expressions into expressions of the expected type.
/// </summary>
internal class SqlBooleanizer {
private class Booleanizer : SqlBooleanMismatchVisitor {
private SqlFactory sql;
internal Booleanizer(TypeSystemProvider typeProvider, MetaModel model) {
this.sql = new SqlFactory(typeProvider, model);
}
internal override SqlSelect VisitSelect(SqlSelect select) {
// DevDiv 179191
if (select.Where != null && select.Where.NodeType == SqlNodeType.Coalesce) {
SqlBinary bin = (SqlBinary)select.Where;
if (bin.Right.NodeType == SqlNodeType.Value) {
SqlValue value = (SqlValue)bin.Right;
if (value.Value != null && value.Value.GetType() == typeof(bool) && (bool)value.Value == false) {
select.Where = bin.Left;
}
}
}
return base.VisitSelect(select);
}
internal override SqlExpression ConvertValueToPredicate(SqlExpression valueExpression) {
// Transform the 'Bit' expression into a 'Predicate' by forming the
// following operation:
// OriginalExpr = 1
// Yukon and later could also handle:
// OriginalExpr = 'true'
// but Sql2000 does not support this.
return new SqlBinary(SqlNodeType.EQ,
valueExpression.ClrType, sql.TypeProvider.From(typeof(bool)),
valueExpression,
sql.Value(typeof(bool), valueExpression.SqlType, true, false, valueExpression.SourceExpression)
);
}
internal override SqlExpression ConvertPredicateToValue(SqlExpression predicateExpression) {
// Transform the 'Predicate' expression into a 'Bit' by forming the
// following operation:
// CASE
// WHEN predicateExpression THEN 1
// ELSE NOT(predicateExpression) THEN 0
// ELSE NULL
// END
// Possible simplification to the generated SQL would be to detect when 'predicateExpression'
// is SqlUnary(NOT) and use its operand with the literal 1 and 0 below swapped.
SqlExpression valueTrue = sql.ValueFromObject(true, false, predicateExpression.SourceExpression);
SqlExpression valueFalse = sql.ValueFromObject(false, false, predicateExpression.SourceExpression);
if (SqlExpressionNullability.CanBeNull(predicateExpression) != false) {
SqlExpression valueNull = sql.Value(valueTrue.ClrType, valueTrue.SqlType, null, false, predicateExpression.SourceExpression);
return new SqlSearchedCase(
predicateExpression.ClrType,
new SqlWhen[] {
new SqlWhen(predicateExpression, valueTrue),
new SqlWhen(new SqlUnary(SqlNodeType.Not, predicateExpression.ClrType, predicateExpression.SqlType, predicateExpression, predicateExpression.SourceExpression), valueFalse)
},
valueNull,
predicateExpression.SourceExpression
);
}
else {
return new SqlSearchedCase(
predicateExpression.ClrType,
new SqlWhen[] { new SqlWhen(predicateExpression, valueTrue) },
valueFalse,
predicateExpression.SourceExpression
);
}
}
}
/// <summary>
/// Rationalize boolean expressions for the given node.
/// </summary>
internal static SqlNode Rationalize(SqlNode node, TypeSystemProvider typeProvider, MetaModel model) {
return new Booleanizer(typeProvider, model).Visit(node);
}
}
}
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