我知道我可以使用投影用 LINQ 映射两种对象类型,如下所示:
var destModel = from m in sourceModel
select new DestModelType {A = m.A, C = m.C, E = m.E}
在哪里
class SourceModelType
{
string A {get; set;}
string B {get; set;}
string C {get; set;}
string D {get; set;}
string E {get; set;}
}
class DestModelType
{
string A {get; set;}
string C {get; set;}
string E {get; set;}
}
但是,如果我想制作类似泛型的东西来做到这一点,我不知道我正在处理的两种类型,该怎么办。所以它会遍历“Dest”类型并与匹配的“Source”类型匹配..这可能吗?此外,为了实现延迟执行,我希望它只返回一个 IQueryable。
例如:
public IQueryable<TDest> ProjectionMap<TSource, TDest>(IQueryable<TSource> sourceModel)
{
// dynamically build the LINQ projection based on the properties in TDest
// return the IQueryable containing the constructed projection
}
我知道这很有挑战性,但我希望不是不可能的,因为它会为我节省大量模型和 View 模型之间的显式映射工作。
最佳答案
你必须生成一个表达式树,但是一个简单的,所以它不是那么难......
void Main()
{
var source = new[]
{
new SourceModelType { A = "hello", B = "world", C = "foo", D = "bar", E = "Baz" },
new SourceModelType { A = "The", B = "answer", C = "is", D = "42", E = "!" }
};
var dest = ProjectionMap<SourceModelType, DestModelType>(source.AsQueryable());
dest.Dump();
}
public static IQueryable<TDest> ProjectionMap<TSource, TDest>(IQueryable<TSource> sourceModel)
where TDest : new()
{
var sourceProperties = typeof(TSource).GetProperties().Where(p => p.CanRead);
var destProperties = typeof(TDest).GetProperties().Where(p => p.CanWrite);
var propertyMap = from d in destProperties
join s in sourceProperties on new { d.Name, d.PropertyType } equals new { s.Name, s.PropertyType }
select new { Source = s, Dest = d };
var itemParam = Expression.Parameter(typeof(TSource), "item");
var memberBindings = propertyMap.Select(p => (MemberBinding)Expression.Bind(p.Dest, Expression.Property(itemParam, p.Source)));
var newExpression = Expression.New(typeof(TDest));
var memberInitExpression = Expression.MemberInit(newExpression, memberBindings);
var projection = Expression.Lambda<Func<TSource, TDest>>(memberInitExpression, itemParam);
projection.Dump();
return sourceModel.Select(projection);
}
(在 LinqPad 中测试,因此
Dump
s)生成的投影表达式如下所示:
item => new DestModelType() {A = item.A, C = item.C, E = item.E}
关于linq - 使用 LINQ 动态映射(或构建投影),我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/2928757/