最简单的方法是这样的。

var book = new Model.Book
{
    BookNumber =  _book.BookNumber,
    BookName = _book.BookName,
    BookTitle = _book.BookTitle,
};
using (var db = new MyContextDB())
{
    var result = db.Books.SingleOrDefault(b => b.BookNumber == bookNumber);
    if (result != null)
    {
        try
        {
            // you can't attach book since it doesn't exist in the database yet
            // attach result instead
            db.Books.Attach(result);
            result = book; // this will update all the fields at once
            db.SaveChanges();
        }
        catch (Exception ex)
        {
            throw;
        }
    }
}

这是实体框架6.2.0。

如果你有一个特定的DbSet和一个需要更新或创建的项:

var name = getNameFromService();

var current = _dbContext.Names.Find(name.BusinessSystemId, name.NameNo);
if (current == null)
{
    _dbContext.Names.Add(name);
}
else
{
    _dbContext.Entry(current).CurrentValues.SetValues(name);
}
_dbContext.SaveChanges();

但是，这也可以用于具有单个主键或复合主键的通用DbSet。

var allNames = NameApiService.GetAllNames();
GenericAddOrUpdate(allNames, "BusinessSystemId", "NameNo");

public virtual void GenericAddOrUpdate<T>(IEnumerable<T> values, params string[] keyValues) where T : class
{
    foreach (var value in values)
    {
        try
        {
            var keyList = new List<object>();

            //Get key values from T entity based on keyValues property
            foreach (var keyValue in keyValues)
            {
                var propertyInfo = value.GetType().GetProperty(keyValue);
                var propertyValue = propertyInfo.GetValue(value);
                keyList.Add(propertyValue);
            }

            GenericAddOrUpdateDbSet(keyList, value);
            //Only use this when debugging to catch save exceptions
            //_dbContext.SaveChanges();
        }
        catch
        {
            throw;
        }
    }
    _dbContext.SaveChanges();
}

public virtual void GenericAddOrUpdateDbSet<T>(List<object> keyList, T value) where T : class
{
    //Get a DbSet of T type
    var someDbSet = Set(typeof(T));

    //Check if any value exists with the key values
    var current = someDbSet.Find(keyList.ToArray());
    if (current == null)
    {
        someDbSet.Add(value);
    }
    else
    {
        Entry(current).CurrentValues.SetValues(value);
    }
}

这段代码是一个测试的结果，该测试只更新了一组列，而没有首先进行查询以返回记录。它首先使用实体框架7代码。

// This function receives an object type that can be a view model or an anonymous 
// object with the properties you want to change. 
// This is part of a repository for a Contacts object.

public int Update(object entity)
{
    var entityProperties =  entity.GetType().GetProperties();   
    Contacts con = ToType(entity, typeof(Contacts)) as Contacts;

    if (con != null)
    {
        _context.Entry(con).State = EntityState.Modified;
        _context.Contacts.Attach(con);

        foreach (var ep in entityProperties)
        {
            // If the property is named Id, don't add it in the update. 
            // It can be refactored to look in the annotations for a key 
            // or any part named Id.

            if(ep.Name != "Id")
                _context.Entry(con).Property(ep.Name).IsModified = true;
        }
    }

    return _context.SaveChanges();
}

public static object ToType<T>(object obj, T type)
{
    // Create an instance of T type object
    object tmp = Activator.CreateInstance(Type.GetType(type.ToString()));

    // Loop through the properties of the object you want to convert
    foreach (PropertyInfo pi in obj.GetType().GetProperties())
    {
        try
        {
            // Get the value of the property and try to assign it to the property of T type object
            tmp.GetType().GetProperty(pi.Name).SetValue(tmp, pi.GetValue(obj, null), null);
        }
        catch (Exception ex)
        {
            // Logging.Log.Error(ex);
        }
    }
    // Return the T type object:         
    return tmp;
}

以下是完整的代码:

public interface IContactRepository
{
    IEnumerable<Contacts> GetAllContats();
    IEnumerable<Contacts> GetAllContactsWithAddress();
    int Update(object c);
}

public class ContactRepository : IContactRepository
{
    private ContactContext _context;

    public ContactRepository(ContactContext context)
    {
        _context = context;
    }

    public IEnumerable<Contacts> GetAllContats()
    {
        return _context.Contacts.OrderBy(c => c.FirstName).ToList();
    }

    public IEnumerable<Contacts> GetAllContactsWithAddress()
    {
        return _context.Contacts
            .Include(c => c.Address)
            .OrderBy(c => c.FirstName).ToList();
    }   

    //TODO Change properties to lambda expression
    public int Update(object entity)
    {
        var entityProperties = entity.GetType().GetProperties();

        Contacts con = ToType(entity, typeof(Contacts)) as Contacts;

        if (con != null)
        {
            _context.Entry(con).State = EntityState.Modified;
            _context.Contacts.Attach(con);

            foreach (var ep in entityProperties)
            {
                if(ep.Name != "Id")
                    _context.Entry(con).Property(ep.Name).IsModified = true;
            }
        }

        return _context.SaveChanges();
    }

    public static object ToType<T>(object obj, T type)
    {
        // Create an instance of T type object
        object tmp = Activator.CreateInstance(Type.GetType(type.ToString()));

        // Loop through the properties of the object you want to convert
        foreach (PropertyInfo pi in obj.GetType().GetProperties())
        {
            try
            {
                // Get the value of the property and try to assign it to the property of T type object
                tmp.GetType().GetProperty(pi.Name).SetValue(tmp, pi.GetValue(obj, null), null);
            }
            catch (Exception ex)
            {
                // Logging.Log.Error(ex);
            }
        }
        // Return the T type object
        return tmp;
    }
}    

public class Contacts
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Email { get; set; }
    public string Company { get; set; }
    public string Title { get; set; }
    public Addresses Address { get; set; }    
}

public class Addresses
{
    [Key]
    public int Id { get; set; }
    public string AddressType { get; set; }
    public string StreetAddress { get; set; }
    public string City { get; set; }
    public State State { get; set; }
    public string PostalCode { get; set; }  
}

public class ContactContext : DbContext
{
    public DbSet<Addresses> Address { get; set; } 
    public DbSet<Contacts> Contacts { get; set; } 
    public DbSet<State> States { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        var connString = "Server=YourServer;Database=ContactsDb;Trusted_Connection=True;MultipleActiveResultSets=true;";
        optionsBuilder.UseSqlServer(connString);
        base.OnConfiguring(optionsBuilder);
    }
}

我一直在审查实体框架的源代码，并找到了一种方法来实际更新一个实体，如果你知道Key属性:

public void Update<T>(T item) where T: Entity
{
    // assume Entity base class have an Id property for all items
    var entity = _collection.Find(item.Id);
    if (entity == null)
    {
        return;
    }

    _context.Entry(entity).CurrentValues.SetValues(item);
}

否则，请检查AddOrUpdate实现以获得想法。

希望这对你有所帮助!

你应该删除db.Books.Attach(book);

你可以使用AddOrUpdate方法:

db.Books.AddOrUpdate(book); //requires using System.Data.Entity.Migrations;
db.SaveChanges();