Question

是否可以将Subsonic 2.1中的多个过滤器组合成一段较短的代码？

    SubSonic.Where filterTaal = 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();

在我看来，上面的代码可以更短？

Answer 1

您可以编写自己的扩展方法并使用ExpressionTrees。结果将是这样的：

PaginaCollection paginaCollection = new PaginaCollection()
    .SlimWhere(x => x[paginaColumns.PaginaKey] == paginaKey)
    .SlimWhere(x => x[paginaColumns.Taal] == taal)
    .Load();

扩展方法将是smth。像这样：

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);
}

辅助方法将是：

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是一个虚拟类，只是为了提供更具可读性的语法，因为.SlimWhere(paginaColumns.PaginaKey == paginaKey)不是那么容易理解。

public class WhereDummy
{
    public string this[string columnname]
    {
        get
        {
            return columnname;
        }
    }
}

组合多个SubSonic.Where过滤器

1 个答案: