使用 Entity Framework 减少数据库调用

Question

是否可以在 1 条语句中编写此代码（仅进行 1 次数据库调用？）并且仍然能够区分 "The member did not exist" 和 "The member did exist but had no dogs"。

public IEnumerable<Dog> GetDogsOfMember(int id)
{
    if (dbContext.Members.Any(i => i.ID == id))
    {
        return dbContext.Dogs.Where(i => i.Member.ID == id);
    }

    return null;
}

Answer 1

如果每个 Dog 已经包含对 Member 的引用，您可以公开关系的另一端（如果您还没有）：

public class Member
{
    public int ID { get; set; }
    // ...
    public virtual ICollection<Dog> Dogs { get; set; }
}

然后您可以使用 Include():

发出单个高效查询

public IEnumerable<Dog> GetDogsOfMember(int id)
{
    var memberWithDogs = dbContext.Members
                                  .Include(i => i.Dogs)
                                  .SingleOrDefault(i => i.ID == id);

    if (memberWithDogs != null)
        return memberWithDogs.Dogs;

    return null;
}

使用 Entity Framework 减少数据库调用

Reduce database calls with Entity Framework

c#

entity-framework

database-performance