C＃MVC ASP.NET从ID为ID的数据库获取数据的最有效方法

Question

I'm new to MVC and databases, but I'm fairly certain the way that I'm getting data from the database is incredibly inefficient.

public class PokemonViewController : Controller
{
    private PokemonDayCareDBEntities1 db = new PokemonDayCareDBEntities1();

    [Authorize]
    public ActionResult Pokemon(int id)
    {
        var pkmn = db.PlayerPkmns.ToList();
        PlayerPkmn thispkmn = null;

        //get pokemon from database where id = id
        foreach (var item in pkmn)
        {
            if (item.Id == id)
            {
                thispkmn = item;
            }
        }

....

I have the unique ID of the Pokemon that resides in the PlayerPkmns table, but I'm looping through the entire table in order to find the matching ID.

Depending on how large the table, the time this takes to execute would increase.

I'm positive there's a better way - would anyone know if there is one (also, the syntax on how to use it)

Thanks!

Answer 1

SingleOrDefault is your friend here.

Change this:

var pkmn = db.PlayerPkmns.ToList();

To

var pkmn = db.PlayerPkmns.SingleOrDefault(x => x.Id == id);

This will translate (roughly) into the following SQL

SELECT TOP 1 * FROM PlayerPkmns WHERE ID = @id

Answer 2

检索实体的最有效方法是使用.Find（），其中primaryKey是您要传入的ID。

var PlayerPkmn= db.PlayerPkmns.Find(primaryKey)

Answer 3

As you are using Linq to Entities, you should be able to use the Where() in combination with FirstOrDefault() :

var pkmn = db.PlayerPkmns.Where(x=>x.Id  == id).FirstOrDefault();

The way you are doing right now will cause all the records to be brought in memory which is not what you want i believe, and it will be much performant than the way you are doing right now, as with the way you are doing, it will load all records in to the memory.

Answer 4

I suppose that PokemonDayCareDBEntities1 is an Entity Framework Data Context . In that case you can use db.PlayerPkmns.Find(id) or db.PlayerPkmns.SingleOrDefault(x => x.Id == id) if you want to handle the case where the entity does not exist in the DB, db.PlayerPkmns.Single(x => x.Id == id) if you are sure that there is strictly one element in the DB (will throw if the entity does not exist).