Entity Framework select single value from row
I am using Entity Framework from .NET 3.5
I have two tables with 0-1 to many relation. Let's say Citizen and City. Each citizen has foreign key column (ID) that connects him to City.
When i select single citizen, i also need to select the name of the city where he lives. Because city table contains tons of data that is not really related to citizen, so i don't want to retrieve it from database to 开发者_开发技巧save some bandwidth.
Currently i am using Include() function, but it grabs all the data from the City related to citizen, while i need only name.
Is there a way to write a query to select single cell from the whole row in EF and without creating new classes or interfaces or repositories? Here is my Include:
Citizen citizen = db.Citizens.Include("Cities").First(p => p.citizen_id == id);
You do this by projecting, e.g.
var c = from c in db.Citizens
where c.citizen_id == id
select new
{
Name = c.Name,
CityName = c.City.Name
};
You can also project onto POCOs.
You cannot tell the EF to retrieve an object of type Citizen
with a related City
but with only City.Name
filled in. The EF will not partially materialize an entity. Use view / presentation models or DTOs instead of entities when you need only a few fields.
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