/// <summary>
/// Private helper to parse a sort expression string and create Comparison delegates based on each property.
/// </summary>
/// <param name="sortExpression">Sort expression to parse.</param>
/// <returns>List of Comparison delegates, one for each property.</returns>
private static List <Comparison <T> > GetFieldComparisons(String sortExpression)
{
SimpleTokenizer parser = new SimpleTokenizer(sortExpression);
List <Comparison <T> > comparisons = new List <Comparison <T> >(4);
List <String> propertyParts = new List <string>(4);
Boolean moreProperties;
do
{
do
{
String property = parser.ReadIdentity();
if (property.Length == 0)
{
throw new ParserException(parser.Position, sortExpression, "Field or property expected");
}
propertyParts.Add(property);
}while (parser.AdvanceIfSymbol('.'));
moreProperties = parser.AdvanceIfSymbol(',');
bool ascending = true;
if (moreProperties == false)
{
if (parser.AdvanceIfIdent(DESC) || parser.AdvanceIfIdent(DESCENDING))
{
ascending = false;
moreProperties = parser.AdvanceIfSymbol(',');
}
else if (parser.AdvanceIfIdent(ASC) || parser.AdvanceIfIdent(ASCENDING))
{
moreProperties = parser.AdvanceIfSymbol(',');
}
}
try
{
comparisons.Add(GetPropertyComparison(propertyParts, ascending));
}
catch (ArgumentException ex)
{
throw new ParserException(parser.Position, parser.Expression, ex.Message);
}
propertyParts.Clear();
}while (moreProperties);
parser.ExpectEnd();
return(comparisons);
}
/// <summary>
/// Sorts the elements of a queryable sequence based on the given search criteria.
/// </summary>
/// <param name="source">The IQueryable sequence to be sorted.</param>
/// <param name="sortExpression">A SQL-like sort expression with comma separated property names (and optional direction specifiers) (e.g. "Age DESC, Name.Length")</param>
/// <returns>A queryable sequence sorted according to the sort expression</returns>
/// <exception cref="System.ArgumentNullException">source or sortExpression is null.</exception>
/// <exception cref="ParserException">if sortExpression is not properly formatted or contains unrecognized property or field names..</exception>
public static IOrderedQueryable <T> OrderBy(IQueryable <T> source, String sortExpression)
{
if (source == null)
{
throw new ArgumentNullException("source");
}
if (sortExpression == null)
{
throw new ArgumentNullException("sortExpression");
}
SimpleTokenizer tokenizer = new SimpleTokenizer(sortExpression);
IQueryable <T> result = source;
List <String> propParts = new List <string>(4);
do
{
ParameterExpression param = Expression.Parameter(typeof(T), "o");
// Create (nested) member access expression.
Expression body = param;
do
{
String property = tokenizer.ReadIdentity();
if (property.Length == 0)
{
throw new ParserException(tokenizer.Position, sortExpression, "Property or field expected.");
}
// Implicitely call Value for Nullable properties/fields.
if (Nullable.GetUnderlyingType(body.Type) != null)
{
body = Expression.Property(body, "Value");
}
MemberInfo member = GetMemberByName(body.Type, property);
if (member == null)
{
throw new ParserException(tokenizer.Position, sortExpression, property + " not a public property or field.");
}
body = Expression.MakeMemberAccess(body, member);
}while (tokenizer.AdvanceIfSymbol('.'));
LambdaExpression keySelectorLambda = Expression.Lambda(body, param);
bool ascending = true;
if (tokenizer.AdvanceIfIdent(DESC) || tokenizer.AdvanceIfIdent(DESCENDING))
{
ascending = false;
}
else if (tokenizer.AdvanceIfIdent(ASC) || tokenizer.AdvanceIfIdent(ASCENDING))
{
ascending = true;
}
String queryMethod;
if (result == source)
{
queryMethod = ascending ? "OrderBy" : "OrderByDescending";
}
else
{
queryMethod = ascending ? "ThenBy" : "ThenByDescending";
}
result = result.Provider.CreateQuery <T>(Expression.Call(typeof(Queryable), queryMethod,
new Type[] { typeof(T), body.Type },
result.Expression,
Expression.Quote(keySelectorLambda)));
}while(tokenizer.AdvanceIfSymbol(","));
tokenizer.ExpectEnd();
return((IOrderedQueryable <T>)result);
}
