Entity Framework——常見報錯總結
1 實體屬性配置為IsRequired()對更新的影響
拋出異常類型DbEntityValidationException
表結構:
實體:
public class User { public int Id { get; set; } /// <summary> /// 賬號 /// </summary> public string Account { get; set; } /// <summary> /// 郵箱 /// </summary>public string Email { get; set; } /// <summary> /// 昵稱 /// </summary> public string Nickname { get; set; } /// <summary> /// 頭像 /// </summary> public string AvatarId { get; set; } /// <summary> /// 記錄插入時間/// </summary> public DateTime InsertTime { get; set; } /// <summary> /// 記錄修改時間 /// </summary> public DateTime UpdateTime { get; set; } }
實體配置:
modelBuilder.Entity<User>().Property(u => u.Account) .IsRequired() .IsUnicode(false) .HasMaxLength(50); modelBuilder.Entity<User>().Property(u => u.Email) .IsRequired() .IsUnicode(false) .HasMaxLength(100); modelBuilder.Entity<User>().Property(u => u.Nickname) .IsUnicode(false) .HasMaxLength(50); modelBuilder.Entity<User>().Property(u => u.AvatarId) .IsOptional() .HasMaxLength(100);
CustomDbContext繼承自DbContext
[DbConfigurationType(typeof(MySqlEFConfiguration))] public class CustomDbContext : DbContext { public CustomDbContext() : base("name=Master") { this.Configuration.LazyLoadingEnabled = false; //DropCreateDatabaseIfModelChanges //new DropCreateDatabaseAlways<CustomDbContext>() Database.SetInitializer<CustomDbContext>(null); } public DbSet<User> Users { get; set; } protected override void OnModelCreating(DbModelBuilder modelBuilder) { base.OnModelCreating(modelBuilder); EntityConfiguration.Set(modelBuilder); } }
更新操作:
using (CustomDbContext db = new CustomDbContext()) { User user = new User { Id = 1, Email = "[email protected]", }; DbEntityEntry<User> entry = db.Entry<User>(user); entry.State = EntityState.Unchanged; entry.Property(t => t.Email).IsModified = true; int num = db.SaveChanges(); }
執行操作,報錯信息如下:
查看EntityValidationErrors,
只能看到{System.Data.Entity.Validation.DbEntityValidationResult},沒有更詳細的信息。
如果將上述代碼用try..catch包起來,如下寫法:
try { //執行代碼 } catch (DbEntityValidationException ex) { var e = ex.EntityValidationErrors; } catch (Exception ex) { }
一層一層地打開,看到真正導致異常的原因,看到下面的截圖:
分析實體配置發現,Account屬性被設置為IsRequired,那麽在更新實體的時候,即使不更新這個字段,也要給這個字段賦值,那麽賦值後觀察:
更新操作代碼變為
using (CustomDbContext db = new CustomDbContext()) { User user = new User { Id = 1, Email = "[email protected]", Account = "a" }; DbEntityEntry<User> entry = db.Entry<User>(user); entry.State = EntityState.Unchanged; entry.Property(t => t.Email).IsModified = true; int num = db.SaveChanges(); }
經過上述調整後,更新成功。
那麽換一個思路,將Account屬性被設置為IsOptional()是不是也可以呢?
修改實體配置,將Account屬性設置按如下修改,並註掉上面的Account = "a"
modelBuilder.Entity<User>().Property(u => u.Account)
.IsOptional()
.IsUnicode(false)
.HasMaxLength(50);
執行測試,更改成功。
得出結論:在實體配置時,指定了為必選的字段,那麽更新操作時,構造實例一定要對必選(IsRequired())字段賦值。
上述測試中還有一個值得考慮的細節,構造User實例的時候,只對Id,Email進行了賦值,而沒有對其他屬性進行賦值,那麽為什麽會成功呢?那麽必定是未進行任何設置的實體屬性默認是IsOptional()。這跟表結構中的字段類型設置為Not Null有無關聯呢,從測試結果看就本類應用無必然聯系。
總結:
a.實體配置中指定了實體屬性為IsRequired(),更新操作構造類的實例時必對此屬性賦值。
b.不進行配置的實體屬性默認為IsOptional()
c.表結構中字段是否為Not Null對上述規則無影響。
2 更新報錯:
An object with the same key already exists in the ObjectStateManager. The ObjectStateManager cannot track multiple objects with the same key.
異常類型:System.Data.Entity.Infrastructure.DbUpdateConcurrencyException
實體屬性配置如上例所示。
操作代碼:
using (CustomDbContext db = new CustomDbContext()) { User user = new User { Id = 1, Email = "[email protected]", }; DbEntityEntry<User> entry = db.Entry<User>(user); entry.State = EntityState.Unchanged; entry.Property(t => t.Email).IsModified = true; User user1 = new User { Id = 1, Email = "[email protected]", }; DbEntityEntry<User> entry1 = db.Entry<User>(user1); entry1.State = EntityState.Unchanged; entry1.Property(t => t.Email).IsModified = true; int num = db.SaveChanges(); }
執行操作
涉及到兩次修改操作,兩次操作構造了兩個實例,但是實例的屬性Id有相同的值。
如果兩次操作的是同一個實例,而不是不同的實例,那麽不會拋出異常,代碼如下:
using (CustomDbContext db = new CustomDbContext()) { User user = new User { Id = 1, Email = "[email protected]", }; DbEntityEntry<User> entry = db.Entry<User>(user); entry.State = EntityState.Unchanged; entry.Property(t => t.Email).IsModified = true; DbEntityEntry<User> entry1 = db.Entry<User>(user); entry1.State = EntityState.Unchanged; entry1.Property(t => t.Email).IsModified = true; int num = db.SaveChanges(); }
3 未給主鍵賦值或賦給主鍵一個不存在的值,拋出異常
System.Data.Entity.Infrastructure.DbUpdateConcurrencyException
操作代碼如下,其中Id=1這條語句被註掉,Id是主鍵:
using (CustomDbContext db = new CustomDbContext()) { User user = new User { //Id = 1, Email = "[email protected]", }; DbEntityEntry<User> entry = db.Entry<User>(user); entry.State = EntityState.Unchanged; entry.Property(t => t.Email).IsModified = true; int num = db.SaveChanges(); }
運行上述代碼,拋出異常信息如下,註意異常類型居然是System.Data.Entity.Infrastructure.DbUpdateConcurrencyException,看上去像是並發問題,但實際卻不是!
Message:
Store update, insert, or delete statement affected an unexpected number of rows (0). Entities may have been modified or deleted since entities were loaded. Refresh ObjectStateManager entries.
賦給主鍵一個不存在的值,令Id=4(在數據庫表中不存在Id為4的一條記錄)拋出的異常與上面的相同。
4 字段超長拋出異常:System.Data.Entity.Validation.DbEntityValidationException
表中Nickname 字段定義為50個字符,現在賦值超過50。
操作代碼如下:
using (CustomDbContext db = new CustomDbContext()) { User user = new User { Id = 4, Email = "[email protected]", Nickname = "TestUpdateErrorTestUpdateErrorTestUpdateErrorTestUpdateErrorTestUpdateErrorTestUpdateErrorTestUpdateErrorTestUpdateErrorTestUpdateErrorTestUpdateErrorTestUpdateError" }; DbEntityEntry<User> entry = db.Entry<User>(user); entry.State = EntityState.Unchanged; entry.Property(t => t.Email).IsModified = true; int num = db.SaveChanges(); }
運行程序報錯:
一層一層點開,查看具體原因:
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Entity Framework——常見報錯總結