Entity Framework - lazy loading or additional async/await query method?

问题

I have these Domain Models

public class Topic
{
    public int TopicId { get; set; }

    public virtual ICollection<Post> Posts { get; set; }
}

public class Post
{
    public int PostId { get; set; }

    public int? TopicId { get; set; }
    public virtual Topic Topic { get; set; }
}

For example I would like to impliment method TestAsync, there I want to work with Topic object and related Posts objects.

Topic model I can get using async method and topicId as param.

public async Task<bool> TestAsync(int topicId)
{
    var topic = await topicService.GetByIdAsync(topicId);

    // posts ...
}

And I have two ways, how to get related posts. But, what the difference if I will use LazyLoading or just another async query?

// Example: 1 (LazyLoading)
var posts = topic.Posts;

// OR Example: 2 (Async method)
var posts = await postService.GetAllByTopicIdAsync(topicId);

So, I think that Example:1 will works synchronously, and also that I lose all the advantages of async/await code. But Example: 2 makes me think, that may be I dont know all charms of Lazy Loading:) Could anyone clarify what solution I should use and why? Thanks:)

回答1:

Lazy loading is always synchronous, which is unfortunate. EF Core, for example, with its async-first mentality, does not (yet) support lazy loading.

Other options are to either do a join (eager loading) as Peter suggested, which asynchronously performs a single query; or to do an explicit second asynchronous query. Which one you'd choose comes down to how your model is normally used.

Personally, I would choose to do the eager loading if the models are always used together, and do multiple asynchronous queries otherwise. I do not use lazy loading myself, though nothing would prevent it from working.

回答2:

You should do neither. I am assuming your GetByIdAsync() is implemented like this.

public async Task<Topic> GetByIdAsync(int id)
{
        return await context.Topics.FirstAsync(t=>t.Id == id);
}

You should change it to be

public async Task<Topic> GetByIdAsync(int id)
{
        return await context.Topics.Include(t=>t.Posts).FirstAsync(t=>t.Id == id);
}

来源：https://stackoverflow.com/questions/45421267/entity-framework-lazy-loading-or-additional-async-await-query-method

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ASP.NET

entity-framework

async-await

lazy-loading