我试图在运行时生成一个简单的Lambda Expression而没有运气......就像这样:
var result = queryableData.Where(item => item.Name == "Soap")
这是我的示例类和fixture可查询:
public class Item
{
public int Id { get; set; }
public string Name { get; set; }
}
IQueryable<Item> queryableData = ...;
然后我在运行时生成一个lambda表达式正确的代码:
//"item" in "item =>..."
var item = Expression
.Parameter(typeof(Item), "item");
//property of my item, this is "item.Name"
var prop = Expression
.Property(item, "Name");
//then "Soap" in '... => item.Name=="Soap"'
var value = Expression.Constant("Soap");
//equality expression "==" in my primer
var equals = Expression.Equal(prop, value);
//then lambda
var lambda = Expression.Lambda<Func<Item, bool>>(equals, item);
//and here are the results
var results = queryableData.Where(lambda);
非常感谢 dtb 提供建议!
答案 0 :(得分:118)
在以下查询中
var result = query.Where(item => item.Name == "Soap")
lambda表达式是
item => item.Name == "Soap"
您只需要构造此部分,而不是接受表达式树的Where调用。
lambda表达式的表达式树如下所示:
Lambda
/ \
Equal Parameter
/ \ item
Property \
"Name" Constant
| "Soap"
Parameter
item
在代码中:
var item = Expression.Parameter(typeof(Item), "item");
var prop = Expression.Property(item, "Name");
var soap = Expression.Constant("Soap");
var equal = Expression.Equal(prop, soap);
var lambda = Expression.Lambda<Func<Item, bool>>(equal, item);
var result = queryableData.Where(lambda);