我正在尝试使用EF6更新记录。首先找到记录，如果它存在，则更新。
这是我的代码:
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
{
db.Books.Attach(book);
db.Entry(book).State = EntityState.Modified;
db.SaveChanges();
}
catch (Exception ex)
{
throw;
}
}
}
每次我尝试使用上面的代码更新记录时，我都会得到这个错误:
{System.Data.Entity.Infrastructure。DbUpdateConcurrencyException:存储
更新、插入或删除语句受影响的数量超出预期
自实体以来，实体可能已被修改或删除
被加载。刷新ObjectStateManager条目
Not related to this specific example, but I came across a challenge when trying to use EF and a DateTime field as the concurrency check field. It appears the EF concurrency code doesn't honor the precision setting from the metadata (edmx) i.e. Type="DateTime" Precision="3".
The database datetime field will store a millisecond component within the field (i.e. 2020-10-18 15:49:02.123). Even if you set the original value of the Entity to a DateTime that includes the millisecond component, the SQL EF generates is this:
UPDATE [dbo].[People]
SET [dateUpdated] = @0
WHERE (([PeopleID] = @1) AND ([dateUpdated] = @2))
-- @0: '10/19/2020 1:07:00 AM' (Type = DateTime2)
-- @1: '3182' (Type = Int32)
-- @2: '10/19/2020 1:06:10 AM' (Type = DateTime2)
正如您所看到的，@2是一个没有毫秒组件的STRING表示。这将导致更新失败。
因此，如果您打算使用DateTime字段作为并发键，那么在检索记录时必须从数据库字段中剥离毫秒/ tick，并且仅使用类似剥离的DateTime传递/更新字段。
//strip milliseconds due to EF concurrency handling
PeopleModel p = db.people.Where(x => x.PeopleID = id);
if (p.dateUpdated.Millisecond > 0)
{
DateTime d = new DateTime(p.dateUpdated.Ticks / 10000000 * 10000000);
object[] b = {p.PeopleID, d};
int upd = db.Database.ExecuteSqlCommand("Update People set dateUpdated=@p1 where peopleId=@p0", b);
if (upd == 1)
p.dateUpdated = d;
else
return InternalServerError(new Exception("Unable to update dateUpdated"));
}
return Ok(p);
当用新值更新字段时，也去掉毫秒
(param)int id, PeopleModel person;
People tbl = db.People.Where(x => x.PeopleID == id).FirstOrDefault();
db.Entry(tbl).OriginalValues["dateUpdated"] = person.dateUpdated;
//strip milliseconds from dateUpdated since EF doesn't preserve them
tbl.dateUpdated = new DateTime(DateTime.Now.Ticks / 10000000 * 10000000);
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);
}
}
