Question

我在使用泛型时遇到麻烦。使用here中的示例，我想传递一个可在EF Core中使用的属性。我觉得我的事情太复杂了。请注意，我想坚持使用lamba表达式，而不是传递诸如nameof之类的东西（我不能在4.0中使用它）。

class Foo
{
        public string A { get; set; } // some unique string in DbSet for entity Person
        public string B { get; set; } // some unique string in DbSet for entity Company

        public int GetId<TEntity>(string match, Expression<Func<TEntity, string>> fieldToExamine,  Expression<Func<TEntity, int>> fieldWithId, System.Data.Entity.DbContext context)
            where TEntity : class
        {
            int retval = -1;
            if (!string.IsNullOrEmpty(match))
            {
                var expr = (MemberExpression)fieldToExamine.Body;
                var prop = (PropertyInfo)expr.Member;
                var expr2 = (MemberExpression)fieldWithId.Body;
                var idField = (PropertyInfo)expr2.Member;
                // this works because everything is explicit
                var entity = context.Set<Person>().SingleOrDefault(p => p.PersonName.Equals(match));
                // ... but I want that to be generic
                // how to reference the property to be evaluated?
                //var entity = context.Set<TEntity>().SingleOrDefault(p => ...); // <- HELP?!
                if (entity != null)
                {
                    retval = (int)entity.GetType().GetProperty(idField.Name).GetValue(entity, null);
                }
            }
            return retval;
        }
}

static void Main(string[] args)
{
// .. omitted database stuff ..
// (for Person) what I want is to match the Name field (here: p.Name) of the Person entity to the Foo property value (here: f.A) and return the database id stored in p.PersonId
int x = f.GetId<Person>(f.A, p => p.PersonName, p => p.PersonId, context);
// same for Company, but different values and fields
int y = f.GetId<Company>(f.B, p => p.CompanyName, p => p.CompanyId, context);
}

Answer 1

head类和Person类将需要实现Company或abstract class。

interface

然后，您可以传递public abstract class BaseEntity { public abstract int Id { get; set; } public abstract string Name { get; set; } } public class Person : BaseEntity { public int PersonId { get; set; } public override string Name { get; set; } public override int Id { get { return PersonId; } set { PersonId = value; } } } public class Company : BaseEntity { public int CompanyId { get; set; } public override string Name { get; set; } public override int Id { get { return CompanyId; } set { CompanyId = value; } } }和p.Name。

p.CompanyId

在lambda表达式中使用的pass属性

1 个答案: