mono/mcs/class/referencesource/System.Data.Linq/SqlClient/Query/SqlBooleanizer.cs

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);
        }
    }
}