Why does adding a parameterless constructor to my entity model class work here? What are the implications?

Question

So I have this office entity class:

[Table("office_entity")]
public class EFOffice : EFBusinessEntity
{

    [Column("address")]
    [StringLength(250)]
    public string Address { get; set; }

    [Column("business_name")]
    [StringLength(150)]
    public string BusinessName { get; set; }

    public virtual ICollection<EFEmployee> Employees { get; set; }

    public EFOffice(Guid id, Guid tenantId, string address, string businessName)
    {
        this.Id = id;
        this.TenantId = tenantId;
        this.Address = address;
        this.BusinessName = businessName;
    }
}

I'm implementing a generic repository, and I just added this method that checks if an entity already exists in the repository:

public bool Exists<TEntity>(Guid key) where TEntity : class, IBusinessEntity
{
    return (_context.Set<TEntity>().Find(key) != null);
}

Then I wrote the following test code:

public void TestExists1()
{
    InitializeDatabase();
    EFOffice testOffice = InitializeOffice1();
    Debug.Assert(EFRepo.Exists<EFOffice>(testOffice.Id));
}

The method for InitializeOffice1() is as follows:

private EFOffice InitializeOffice1()
{
    EFOffice newOffice = new EFOffice(SparkTest.TestGuid1, SparkTest.TestGuid2, "Generic Address", "HQ");
    return newOffice;
}

The test is supposed to pass because I already inserted the office returned by InitializeOffice1() previously. However, I get the following error:

System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.InvalidOperationException: The class 'Models.Employees.EF.EFOffice' has no parameterless constructor.

So then I added this to the EFOffice class shown at the top:

private EFOffice()
{

}

And for some reason the test now passes. Can anyone explain what's going on? And does having a parameterless constructor have bad side effects? It's important that every office I insert has an id, a tenantId, an address and a businessName, as listed in the constructor at the top.

Answer 1

All Entities linked to EntityFramework must have a Default Constructor.

When Entity Framework maps from a database query to your Entities use the default constructor to instantiate a new instance of your Entity to fill it with the data retrieved from your database.

If you don't have a default constructor Entity Framework doesn't know how to create an instance of it and throws the exception

The class 'Models.Employees.EF.EFOffice' has no parameterless constructor.