EF＆Linq无法检索相关数据

Question

I have the current entity class Timesheet :

public class Timesheet
{
    #region Properties
    public int Id { get; set; }
    public DateTime TransactionDate { get; set; }
    public int ProjectId { get; set; }
    public int AccountId { get; set; }
    [MaxLength(50)]
    public string Supplier { get; set; }
    #endregion

    #region Navigation Properties
    [ForeignKey("ProjectId")]
    public virtual Project CurrentProject { get; set; }
    [ForeignKey("AccountId")]
    public virtual Account CurrentAccount { get; set; }
    #endregion
}

When executing this simple query,

var query = db.Timesheets.AsQueryable();
var data = query;
return data;

I get the following results (note CurrentProject and CurrentAccount ):

<Timesheet>
    <AccountId>33</AccountId>
    <CurrentAccount i:nil="true"/>
    <CurrentProject i:nil="true"/>
    <Id>1</Id>
    <ProjectId>1064</ProjectId>
    <Supplier>Test Supplier</Supplier>
    <TransactionDate>2016-02-27T00:00:00</TransactionDate>
</Timesheet>

However, when trying to explicitly load related objects,

var query = db.Timesheets.AsQueryable();
var data = query.Include(n => n.CurrentProject);
return data;

I get a serialization error:

The 'ObjectContent 1' type failed to serialize the response body for content type 'application/xml; charset=utf-8'

<ExceptionMessage> Type 'System.Data.Entity.DynamicProxies.Timesheet_B61B0CCFFB38C448231EBA3EF4D3D57C851AD2AE97FAA0BF8AA7F175D4C507D6' with data contract name 'Timesheet_B61B0CCFFB38C448231EBA3EF4D3D57C851AD2AE97FAA0BF8AA7F175D4C507D6: http://schemas.datacontract.org/2004/07/System.Data.Entity.DynamicProxies ' is not expected. Consider using a DataContractResolver or add any types not known statically to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to DataContractSerializer. </ExceptionMessage>

I ran a similar query using LINQPad and got correct results with all the related objects so I don't know what's wrong here.

I'm a n00b here and can really use your help!

Answer 1

It's almost certainly due to a navigation property from Project back to the Timesheet.

When Timesheet is being serialized, so is the CurrentProject property. That, in turn, references the Timesheet, resulting in a circular reference.

Decorate the Timesheet navigation property on Project class to prevent it being serialized: [JsonIgnore] . You'll have to do the same with the Account class if you .Include() that, too.