Entity Framework adds duplicate entities in database

Question

I'm having a problem with Entity Framework 5 and MVC C# 4.

I have a model (medical) 'Measurement' with the following properties:

[DataMember]
public int ID { get; set; }

[Required]
[DataMember(IsRequired = true)]
[Column(TypeName = "DateTime2")]
public DateTime Date { get; set; }

[Required]
[DataMember(IsRequired = true)]
public Status Status { get; set; }

[Required]
[DataMember(IsRequired = true)]
public User User { get; set; }

[Required]
[DataMember(IsRequired = true)]
public virtual List<Result> Results { get; set; }

The model Result is like this:

[DataMember]
public int ID { get; set; }

[DataMember]
public int Revision { get; set; }

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

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

[DataMember]
public int ValueInt { get; set; }

[Required]
[DataMember]
public virtual MeasurementType MeasurementType { get; set; }

And the model MeasurementType (like Length, Age, Sex, Bloodpressure) is:

public int ID { get; set; }

[Required]
[DataMember]
public string Name { get; set; }

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

I've got a Repository for the connection with the DbContext. When I want to add a new Measurement, the MeasurementType, User, Company and Roles (both in User) are also added into the database, but they are already present in the DB. Result is that there are a lot of duplicates of MeasurementType and Users

This is the method for adding a new measurement:

public void Post(Measurement measurement)
{
    db.Measurements.Add(measurement);
    db.SaveChanges();
}

I know the problem, the EntityState of Measurement.User and Result.MeasurementType has to be Unchanged in stead of Added, but I can't get them on Unchanged. I've tried several solutions found here on SO like Attach(Measurement.MeasurementType) but that give me an error like "An object with the same key is already in the ObjectStateManager".

What have I done wrong? Is it the model or the relationships between Measurement and MeasurementType (many-to-many) or is the error in the Repository-method or is the use of the keyword 'Virtual' not the best method?

@User3805967 They're automatically generated by Entity Framework. — Pino112
– Pino112, Commented Dec 9, 2013 at 10:58
Why does Entity Framework Reinsert Existing Objects into My Database? msdn.microsoft.com/en-us/magazine/dn166926.aspx — Colin
– Colin, Commented Dec 9, 2013 at 11:04

Marthijn · Accepted Answer · 2013-12-09 12:32:29Z

2

You have to create your foreign keys explicitly, for example:

public int UserId { get; set; }
public virtual User User { get; set; }

Then you can do:

User u = GetUserById(1);
myMeasurement.UserId = u.Id;

answered Dec 9, 2013 at 12:32

Marthijn

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