private Expression MapStringLikeExpression(MethodCallExpression node, bool matchStart, bool matchEnd)
{
var expression = base.VisitMethodCall(node) as MethodCallExpression;
if ((expression.Arguments == null) || (expression.Arguments.Count != 1))
{
throw new ApplicationException("Did not find exactly 1 Argument to StartsWith function");
}
DbExpression srcExpression = GetDbExpressionForExpression(expression.Object);
DbExpression dbExpression;
if (expression.Arguments[0] is ConstantExpression)
{
var constantExpression = GetDbExpressionForExpression(expression.Arguments[0]) as DbConstantExpression;
if ((constantExpression == null) || (constantExpression.Value == null))
{
throw new NullReferenceException("Parameter to StartsWith cannot be null");
}
string value = matchStart ? "" : "%";
value += constantExpression.Value.ToString();
if (!matchEnd)
{
value += "%";
}
dbExpression = DbExpressionBuilder.Like(srcExpression, DbExpressionBuilder.Constant(value));
}
else
{
var argExpression = GetDbExpressionForExpression(expression.Arguments[0]);
// Note: Can also do this using StartsWith function on srcExpression (which avoids having to hardcode the % character).
// It works but generates some crazy conditions using charindex which I don't think will use indexes as well as "like"...
//dbExpression = DbExpressionBuilder.Equal(DbExpressionBuilder.True, srcExpression.StartsWith(argExpression));
DbExpression value = matchStart ? argExpression : DbExpressionBuilder.Constant("%").Concat(argExpression);
if (!matchEnd)
{
value = value.Concat(DbExpressionBuilder.Constant("%"));
}
dbExpression = DbExpressionBuilder.Like(srcExpression, value);
}
MapExpressionToDbExpression(expression, dbExpression);
return(expression);
}
