c# – 使用Expression创建带嵌套类的谓词
发布时间:2020-12-15 18:08:13 所属栏目:百科 来源:网络整理
导读:我有这个 : public class Company{ public int Id { get; set; } public string Name { get; set; }}public class City{ public int Id { get; set; } public string Name { get; set; } public int ZipCode { get; set; }}public class Person{ public int
我有这个 :
public class Company { public int Id { get; set; } public string Name { get; set; } } public class City { public int Id { get; set; } public string Name { get; set; } public int ZipCode { get; set; } } public class Person { public int Id { get; set; } public string FirstName { get; set; } public string LastName { get; set; } public int? Age { get; set; } public City City { get; set; } public Company Company { get; set; } } 我想在某种情况下生成这样的谓词: var result = listPerson.Where(x => x.Age == 10).ToList<>(); 或这个 : var result = listPerson.Where( x => x.Company.Name == 1234).ToList(); 或这个 : var result = listPerson.Where( x => x.City.ZipCode == "MyZipCode").ToList(); 或这个 : var result = listPerson.Where( x => x.Company.Name == "MyCompanyName").ToList(); 然后我创建了一个“PredicateBuilder”,这是我的工作(我得到类型,如果可以为空,我构建谓词)当我这样做时: BuildPredicate<Person>("Age",10); I get this : x => x.Age == 10 但是当我有这样的嵌套属性时,我不会如何管理: BuildPredicate<Person>("City.ZipCode","MyZipCode"); I'd like get this : x => x.City.ZipCode == "MyZipCode" 或这个 : BuildPredicate<Person>("City.Name","MyName"); I'd like get this : x => x.City.Name == "MyName" 或这个 : BuildPredicate<Person>("Company.Name","MyCompanyName"); I'd like get this : x => x.Company.Name == "MyCompanyName" 解决方法
(不打算复制Jon – OP联系我提供答案)
以下似乎工作正常: static Expression<Func<T,bool>> BuildPredicate<T>(string member,object value) { var p = Expression.Parameter(typeof(T)); Expression body = p; foreach (var subMember in member.Split('.')) { body = Expression.PropertyOrField(body,subMember); } return Expression.Lambda<Func<T,bool>>(Expression.Equal( body,Expression.Constant(value,body.Type)),p); } 这和Jon的答案之间唯一的区别在于它通过告诉Expression.Constant预期的类型是什么来稍微处理null.作为使用示范: static void Main() { var pred = BuildPredicate<Person>("City.Name","MyCity"); var people = new[] { new Person { City = new City { Name = "Somewhere Else"} },new Person { City = new City { Name = "MyCity"} },}; var person = people.AsQueryable().Single(pred); } (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |