在Asp.Net Web Api中的EntityFramework中查找表对象实体以获得更新前的列的当前值

Question

I`m new in MVC and want to know how to find a Table object entity using where just before updation. My code is as follows:-

    public async Task<IHttpActionResult> PutEmployee(int id, Employee model)
{
    Employee emp = db.Employee.Where(x => x.Id == id).FirstOrDefault();
    if(emp!=null)
    {
        if(emp.ImagePath!=model.ImagePath)
        {
            //Code to move image
        }
        db.Entry(model).State = EntityState.Modified; //THIS IS WHERE IT THROWS ERROR
        model.ImagePath = model.ImagePath.Replace("Temp/", "");
        db.Entry(model).Property(x => x.IsDeleted).IsModified = false;
        //Update changes using db.SaveChanges();
    }
}

Code throws error on db.Entry(model).State = EntityState.Modified;

Attaching an entity of type 'MyProject.Models.Employee' failed because another entity of the same type already has the same primary key value. This can happen when using the 'Attach' method or setting the state of an entity to 'Unchanged' or 'Modified' if any entities in the graph have conflicting key values. This may be because some entities are new and have not yet received database-generated key values. In this case use the 'Add' method or the 'Added' entity state to track the graph and then set the state of non-new entities to 'Unchanged' or 'Modified' as appropriate

The purpose here is to check if Employee with Id exists and if it exists then check whether the current value of Employee.ImagePath is different from the model passed by the User.

Any help will be appreciated...

Answer 1

You don't need to tell the DbContext that the state has changed, it will do that by itself if you change any property. So drop (both) lines where you are doing so.