Combining multiple SubSonic.Where filters
Is it possible to combine multiple filters in Subsonic 2.1 to a shorter piece of code?
SubSonic.Where filterTaal =开发者_运维百科 new SubSonic.Where();
filterTaal.ColumnName = Pagina.Columns.Taal;
filterTaal.Comparison = SubSonic.Comparison.Equals;
filterTaal.ParameterValue = taal;
SubSonic.Where filterKey = new SubSonic.Where();
filterKey.ColumnName = Pagina.Columns.PaginaKey;
filterKey.Comparison = SubSonic.Comparison.Equals;
filterKey.ParameterValue = paginaKey;
PaginaCollection paginaCollection = new PaginaCollection()
.Where(filterTaal)
.Where(filterKey)
.Load();
It seems to me that above code can be shorter?
You could write your own extension method and use ExpressionTrees. Result will be something like this:
PaginaCollection paginaCollection = new PaginaCollection()
.SlimWhere(x => x[paginaColumns.PaginaKey] == paginaKey)
.SlimWhere(x => x[paginaColumns.Taal] == taal)
.Load();
The extension method will be smth. like this:
public static PaginaCollector SlimWhere(this PaginaCollector paginaCollector, Expression<Func<WhereDummy, bool>> expression)
{
var mainExpression = expression.Body as BinaryExpression;
SubSonic.Where result = ParseFilter(mainExpression);
switch (mainExpression.NodeType)
{
case ExpressionType.Equal:
result.Comparison = Comparison.Equals;
break;
...
default:
throw new NotImplementedException();
}
return paginaCollector.Where(result);
}
And the helper methods will be:
private static SubSonic.Where ParseFilter(BinaryExpression expression)
{
var columnNameMethod = (MethodCallExpression)expression.Left;
var columnNameExpression = columnNameMethod.Arguments[0];
var parameterValueExpression = expression.Right;
string columnName = GetValue<string>(columnNameExpression);
object parameterValue = GetValue<object>(parameterValueExpression);
Where result = CreateWheteFilterDummy(columnName, parameterValue);
return result;
}
private static Where CreateWheteFilterDummy(string columnName, object parameterValue)
{
SubSonic.Where result = new Where();
result.ColumnName = columnName;
result.ParameterValue = parameterValue;
return result;
}
private static T GetValue<T>(Expression columnNameExpression)
{
var columnNameObjectMember = Expression.Convert(columnNameExpression, typeof(T));
var columnNameGetter = Expression.Lambda<Func<T>>(columnNameObjectMember);
return columnNameGetter.Compile()();
}
WhereDummy
is a dummy class only to provide more readable syntax, because .SlimWhere(paginaColumns.PaginaKey == paginaKey)
is not so understandable.
public class WhereDummy
{
public string this[string columnname]
{
get
{
return columnname;
}
}
}
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