LINQ to Entities-将所有相关实体字段转换为字符串

Question

I have a Person Entity something like that

PersonId
PersonName
PersonPhone

I have a House Entity

HouseID
HouseType
HouseSize

Both Entities are related with many to many relation. I need to have all the HouseType for a person (which has many houses) into a string.

Answer 1

You can easily concatenate multiple strings from a sequence with the Enumerable.Aggregate method.

In your case you'll have to first project the list of House entities into a list of House.HouseType strings and then aggregate them into a single string:

var houseTypes = person.Houses.Select(i => i.HouseType).AsEnumerable();
var emptyResult = "0";

return houseTypes.Any() ?
    houseTypes.Select(i => i.ToString())
              .Aggregate((current, next) => current + ", " + next) :
    emptyResult;

Alternatively you could simply say:

var houseTypes = person.Houses
                       .Select(i => i.HouseType)
                       .AsEnumerable()
                       .Select(i => i.ToString());
return String.Join(", ", houseTypes);

which will return an empty string when the houseTypes sequence is empty.

Update:

If you're using Entity Framework 4 or above, you can use one of the built-in SQL functions to perform the conversion to string directly in the database:

var houseTypes = person.Houses
                       .Select(i => SqlFunctions.StringConvert((double)i.HouseType))
                       .AsEnumerable()
return String.Join(", ", houseTypes);

Answer 2

You mean something like?:

var data = context.People.Where(p => p.PersonId == <id>).SelectMany(p => p.Houses).Select(h => h.HouseType);
var result = string.Join(<separator>, data);

Answer 3

var houseTypes = person.Houses
    .Select(i => i.HouseType).ToList();

return string.Join(" ", houseTypes.Select(x=>x.ToString()));