Getting a circular reference error in entity framework

Question

I get an error as below:

'Object graph for type 'System.Collections.Generic.HashSet`1[[ERP_Lite_Data.
MenuItem, ERP_Lite_Data, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]' 
contains cycles and cannot be serialized if reference tracking is disabled.

I have a table called MenuItems in my database. The fields and relationships in MenuItems is displayed in the image below:

enter image description here

The Class for this table generated by entity framework is as follows:

public partial class MenuItem
{
    public MenuItem()
    {
        this.MenuItems1 = new HashSet<MenuItem>();
    }

    public int MenuItemID { get; set; }
    public string Title { get; set; }
    public Nullable<int> ParentID { get; set; }

    public virtual ICollection<MenuItem> MenuItems1 { get; set; }
    public virtual MenuItem MenuItem1 { get; set; }
}

I searched for the above error on internet and everywhere I get the same solution of applying DataMember attribute to the members of the class.So I have done that. Here is the modified MenuItem.cs.

[DataContract]    
public partial class MenuItem
{
    public MenuItem()
    {
        this.MenuItems1 = new HashSet<MenuItem>();
    }

    [DataMember, Key]
    public int MenuItemID { get; set; }

    [DataMember]
    public string Title { get; set; }

    [DataMember]
    public Nullable<int> ParentID { get; set; }

    [DataMember]
    public virtual ICollection<MenuItem> MenuItems1 { get; set; }

    [DataMember]
    public virtual MenuItem MenuItem1 { get; set; }
}

But still I get the same error. Can anybody suggest me some workaround?

Update:

If I use the below method to return all the menuitems it works fine:

public IEnumerable<MenuItem> GetAllMenuItems()
{
    using (Entities db = new Entities())
    {
        return (from m in db.MenuItems
                select m).ToList();
    }
}

The moment I change it to something like :

public IEnumerable<MenuItem> GetAllMenuItems()
{
    using (Entities db = new Entities())
    {
        return (from m in db.MenuItems
                select new MenuItem
                {
                    MenuItemID = m.MenuItemID,
                    Title = m.Title,
                    ParentID = m.ParentID
                }).ToList();
    }
}

I get another error:

The entity or complex type 'Models.MenuItem' cannot be constructed in a LINQ to Entities query.

you may ask me to write code like below:

return (from m in db.MenuItems
        select new 
        {
            MenuItemID = m.MenuItemID,
            Title = m.Title,
            ParentID = m.ParentID
        }).ToList();

Then what should be the return type of my method?

Petur Subev · Accepted Answer · 2015-08-20T18:47:53.383

2

Most famous question out there when it comes to serializing. Use projection into some type that does not have such references and avoid the exception.

In other words, pick up just the properties that you need from the EF model, do not add fields which are nested complex types that also have properties that point back to the same object and thus create circular references.

edited Aug 20 '15 at 18:47

answered Mar 01 '14 at 21:06

Petur Subev

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I am a newbie to entity framework, can you explain what do you mean by Data Transport Type? – Vishal Mar 01 '14 at 21:09
Ok, the meaning of different projections is that I should not use select all(*), instead I should select by using column names even if I want to select all columns? – Vishal Mar 01 '14 at 21:15
I have tried the solution you suggested. But I get another error. Please see my Update in question. – Vishal Mar 01 '14 at 21:25
I have solved the second error by using Data Transfer Object(DTO). I found it at http://stackoverflow.com/questions/5325797/the-entity-cannot-be-constructed-in-a-linq-to-entities-query – Vishal Mar 01 '14 at 21:36

Getting a circular reference error in entity framework

1 Answers1