c# Entity Framework Eager Loading 拉入所有孩子

Question

I have this questionGroup that looks something like this:

public class QuestionGroup
{
    public int Id { get; set; }
    [Required] [MaxLength(255)] public string Text { get; set; }
    public QuestionGroupType Type { get; set; }

    public IList<Question> Questions { get; set; }
}

and the question model looks something like this:

public class Question
{
    public int Id { get; set; }
    [Required] [MaxLength(255)] public string Text { get; set; }
    public int QuestionGroupId { get; set; }

    public QuestionGroup QuestionGroup { get; set; }
}

I have disabled Lazy Loading in my DbContext like this:

/// <summary>
/// Default constructor
/// </summary>
public DatabaseContext()
    : base("DefaultConnection")
{

    // Disable Lazy Loading
    this.Configuration.LazyLoadingEnabled = false;

    // Write our SQL to the debug window
    this.Database.Log = s => Debug.WriteLine(s);

    // Increase the timeout
    this.Database.CommandTimeout = 10000;
}

Now, I have a Repository class that has a List method which looks like this:

/// <summary>
/// Gets all the entities
/// </summary>
/// <param name="includes">Option includes for eager loading</param>
/// <returns></returns>
public IQueryable<T> List(params string[] includes)
{

    // Create a query
    IQueryable<T> query = this.dbEntitySet;

    // For each include, append to our query
    foreach (var include in includes)
        query = query.Include(include);

    // Return our query
    return query;
}

So that in theory I can send an array of includes to the Repository so that they can be Eagerly loaded . Somewhere done the line I do this:

var models = await this._service.ListAllAsync("Questions");

Which I would expect to return my QuestionGroups and the child Questions for each group. The problem is, it doesn't just do that, it will Get the Question's group and the groups Question and so on and so on.

like this:

QuestionGroup > Questions > [0] > QuestionGroups > Questions

Does anyone know why and how to stop it?

---

Update

Ok, so now I have enabled Lazy loading and I still get the same issue:

public class QuestionGroup
{
    public int Id { get; set; }
    [Required] [MaxLength(255)] public string Text { get; set; }
    public QuestionGroupType Type { get; set; }

    public virtual IList<Question> Questions { get; set; }
}

A QuestionGroup has one navigational property: Questions

public class Question
{
    public int Id { get; set; }
    [Required] [MaxLength(255)] public string Text { get; set; }
    public int QuestionGroupId { get; set; }

    public QuestionGroup QuestionGroup { get; set; }
    public virtual IList<Answer> Answers { get; set; }
    public virtual Criteria Criteria { get; set; }
}

A Question has 2 navigational properties: Answers and Criteria :

public class Answer
{
    public int Id { get; set; }
    [Required] [MaxLength(255)] public string Text { get; set; }
    public int QuestionId { get; set; }
    public int Order { get; set; }

    public Question Question { get; set; }
    public virtual IList<State> States { get; set; }
}

public class Criteria
{
    public int Id { get; set; }
    [Required] public CriteriaType Type { get; set; }
    [Required] [MaxLength(100)] public string Name { get; set; }
    public bool SaveToDatabase { get; set; }

    public virtual IList<State> States { get; set; }
    public IList<Question> Questions { get; set; }
}

An Answer has one navigational property: States , and Criteria also has one navigational property which also happens to be States :

public class State
{
    public int Id { get; set; }
    public int CriteriaId { get; set; }
    [Required] [MaxLength(100)] public string Name { get; set; }
    public TargetType Target { get; set; }

    public virtual IList<Filter> Filters { get; set; }
    public Criteria Criteria { get; set; }
}

A State has one navigational property, which is Filter :

public class Filter
{
    public int Id { get; set; }
    [Required] [MaxLength(5)] public string Operator { get; set; }
    [Required] [MaxLength(255)] public string Expression { get; set; }
    [MaxLength(100)] public string Field { get; set; }
    public int StateId { get; set; }

    public State State { get; set; }
}

and Filters have no navigational properties. When I try to use Lazy Loading , I expect that only my navigation properties will be populated, but if I try to get the QuestionGroup , it will get the Question with all it's Answers and Criteria , which is fine, but it also get's the QuestionGroup too.

Answer 1

You break the uni-directional navigation by replacing

public QuestionGroup QuestionGroup { get; set; }

with

public int QuestionGroupId { get; set; }

This allows you to query back to get the question group of the question, but not cause a circular reference. You can even encapsulate the query in a method.

public QuestionGroup GetQuestionGroup();