我正在创建一个通用,其中过滤器到目前为止效果很好(仅对Contains
过滤感兴趣):
private static MethodInfo contains = typeof(string).GetMethod("Contains");
private static Expression<Func<T, bool>> GetFilter<T>(string propertyName, string value)
{
var item = Expression.Parameter(typeof(T), "item");
var member = Expression.Property(item, propertyName);
var constant = Expression.Constant(value);
var body = Expression.Call(member, contains, constant);
return Expression.Lambda<Func<T, bool>>(body, item);
}
有什么办法可以扩展它,以便可以通过导航属性进行搜索?我对使用Expression
的新手很新,所以我不确定该尝试什么。
一个例子是:
public class A
{
public int BId { get; set; }
public B B { get; set; }
}
public class B
{
public string Name { get; set; }
}
dbContext.As
.Where(GetFilter<A>("B.Name", "Hello World"))
.ToList();
但这在Expression.Property("B.Name")
上失败了:
实例属性
定义B.Name
未针对A
您需要对属性路径中的每个属性顺序创建每个成员访问:
private static Expression<Func<T, bool>> GetFilter<T>(string propertyName, string value)
{
var item = Expression.Parameter(typeof(T), "item");
Expression member = item;
foreach (var prop in propertyName.Split('.'))
{
member = Expression.Property(member, prop);
}
var constant = Expression.Constant(value);
var body = Expression.Call(member, contains, constant);
return Expression.Lambda<Func<T, bool>>(body, item);
}