Question

Is it possible to create Linq Queries at runtime. Using an xml rule which can be translated to a Linq Query.

Answer 1

归根到底,是的;但是,这并不简单,你需要:

learn the Expression API
use the pre-rolled dynamic LINQ library (from the samples download)

如果你想选择第一种办法,那么你就需要创建自己的lam;例如,想象你们有这样的东西(在这里做事情......):

<Filters>
    <Add Prop="Foo">My filter value</Add>
</Filters>

然后,你们需要做这样的事情:

XElement filters = ...; // the "Filters" element
IQueryable<Customer> query = ...; // your raw (unfiltered) query
foreach(var filter in filters.Elements("Add")) {
    var param = Expression.Parameter(typeof(Customer), "row");
    var body = Expression.Equal(
        Expression.PropertyOrField(param, (string)filter.Attribute("Prop")),
        Expression.Constant(filter.Value, typeof(string)));
    query = query.Where(Expression.Lambda<Func<Customer, bool>>(
        body, param));
}

以上(每个“Add”要素)都产生了一个将特定成员过滤到供应价值(假设体内,但你当然可以做任何转换等)。所有其他行动都是有益的,但效果不大。注:query通过该休息室受到限制。

Answer 2

是的。我不想告诉你如何教化XML,但你可以照此附上林克推广方法:

var IQueryable<bla> query = myDataContext.BlahTable;  // I think you can also use IEnumerable.

if(/* something */)
{
    query = query.Where(b => b.Field1 > 0);
}

if(/* something else */)
{
    query = query.OrderBy(b => b.Field2);
}

Answer 3

基本上,你们需要建设一种表达的树木。在此作简要解释,以回答另一个问题:,从XML 上 trees树。

友情链接