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using System;
using System.Collections.Generic;
using System.Text;
using System.Data.Linq;
namespace System.Data.Linq.SqlClient {
/// <summary>
/// After retyping and conversions take place, some functions need to be changed into more suitable calls.
/// Example: LEN -> DATALENGTH for long text types.
/// </summary>
internal class SqlMethodTransformer : SqlVisitor {
protected SqlFactory sql;
internal SqlMethodTransformer(SqlFactory sql) {
this.sql = sql;
}
internal override SqlExpression VisitFunctionCall(SqlFunctionCall fc) {
// process the arguments
SqlExpression result = base.VisitFunctionCall(fc);
if (result is SqlFunctionCall) {
SqlFunctionCall resultFunctionCall = (SqlFunctionCall)result;
if (resultFunctionCall.Name == "LEN") {
SqlExpression expr = resultFunctionCall.Arguments[0];
if (expr.SqlType.IsLargeType && !expr.SqlType.SupportsLength) {
result = sql.DATALENGTH(expr);
if (expr.SqlType.IsUnicodeType) {
result = sql.ConvertToInt(sql.Divide(result, sql.ValueFromObject(2, expr.SourceExpression)));
}
}
}
// If the return type of the sql function is not compatible with
// the expected CLR type of the function, inject a conversion. This
// step must be performed AFTER SqlRetyper has run.
Type clrType = resultFunctionCall.SqlType.GetClosestRuntimeType();
bool skipConversion = SqlMethodTransformer.SkipConversionForDateAdd(resultFunctionCall.Name,
resultFunctionCall.ClrType,
clrType);
if ((resultFunctionCall.ClrType != clrType) && !skipConversion) {
result = sql.ConvertTo(resultFunctionCall.ClrType, resultFunctionCall);
}
}
return result;
}
internal override SqlExpression VisitUnaryOperator(SqlUnary fc) {
// process the arguments
SqlExpression result = base.VisitUnaryOperator(fc);
if (result is SqlUnary) {
SqlUnary unary = (SqlUnary)result;
switch (unary.NodeType) {
case SqlNodeType.ClrLength:
SqlExpression expr = unary.Operand;
result = sql.DATALENGTH(expr);
if (expr.SqlType.IsUnicodeType) {
result = sql.Divide(result, sql.ValueFromObject(2, expr.SourceExpression));
}
result = sql.ConvertToInt(result);
break;
default:
break;
}
}
return result;
}
// We don't inject a conversion for DATEADD if doing so will downgrade the result to
// a less precise type.
//
private static bool SkipConversionForDateAdd(string functionName, Type expected, Type actual) {
if (string.Compare(functionName, "DATEADD", StringComparison.OrdinalIgnoreCase) != 0)
return false;
return (expected == typeof(DateTime) && actual == typeof(DateTimeOffset));
}
}
}
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