当我尝试将记录更新到数据库时,我收到以下错误：

Store update,insert,or delete statement affected an unexpected
number of rows (0). Entities may have been modified or deleted since
entities were loaded

使用从数据库实体框架模型首先使用代码生成的标准代码时出现此错误.很奇怪,因为我正在使用一台其他人无法访问的独立机器.

这是失败的代码：

if (ModelState.IsValid)
{
    db.Entry(tblPropGroup).State = EntityState.Modified;
    db.SaveChanges();
    return RedirectToAction("Index");
}

所以我写了下面的工作,一段时间完美无缺：

if (ModelState.IsValid)
{
db.Entry(_Prop).State = EntityState.Modified;
bool saveFailed;
do
{
 saveFailed = false;
 try
 {
 db.SaveChanges();
 }
 catch (dbupdateConcurrencyException ex)
 {
 saveFailed = true;
 // Update original values from the database 
 var entry = ex.Entries.Single();
 entry.OriginalValues.SetValues(entry.GetDatabaseValues());
 }
} while (saveFailed);

谁能解释为什么db.SaveChanges在没有其他用户的数据库上导致dbupdateConcurrencyException？如果我对数据进行任何更改,则没有任何区别.我有22个不同的表,我可以在这个程序中访问,如果没有这个解决方法,大约一半不会工作.

以下是一些答案：
side-effect of a feature called optimistic concurrency

Store update,or delete statement affected an unexpected number of rows (0) EntityFramework

这可能有所帮助.

最好使用：

using(DBContext context = new DBContext())
{
    //Entity code
}

处理您的上下文.

public void testValidateInvalidExternalQuestion() throws Exception {
  HITQuestion htmlQuestion = new HITQuestion(defaultInvalidExternalQuestionFileName);

  try {
    service.previewHIT(defaultHITInput,defaultHITProperties,htmlQuestion);

    fail("Expected ValidationException when previewing HIT with invalid external question." );
  }
  catch (ValidationException e) {
    // Expected exception
  }
}

public void testValidateInvalidHTMLQuestion() throws Exception {
  // HTMLQuestion has invalid FrameHeight
  try {
    QAPValidator.validateFile(defaultInvalidHTMLQuestionFileName);
    fail("Expected ValidationException when previewing a HIT with an invalid HTMLQuestion");
  } catch (ValidationException e) {
    // Expected exception
    assertContains("ValidationFailure was not caused by an invalid frame height.","'I am not a number; I am a free man!' is not a valid value for 'integer'",e.getMessage());
  }
}

public void testCreateInvalidFormattedContentHIT() throws Exception {
  HITQuestion htmlQuestion = new HITQuestion(defaultInvalidFormattedContentQuestionFileName);

  try {
    service.previewHIT(defaultHITInput,htmlQuestion);

    fail("Expected ValidationException when creating HIT with invalid formatted content." );
  }
  catch (ValidationException e) {
    // Expected exception
  }
}

public void testCreateScriptFormattedContentHIT() throws Exception {
  HITQuestion htmlQuestion = new HITQuestion(defaultScriptFormattedContentQuestionFileName);

  try {
    service.previewHIT(defaultHITInput,htmlQuestion);

    fail("Expected ValidationException when creating HIT with script in formatted content." );
  }
  catch (ValidationException e) {
    // Expected exception
  }
}

public void testValidateInvalidExternalQuestion() throws Exception {
  HITQuestion htmlQuestion = new HITQuestion(defaultInvalidExternalQuestionFileName);

  try {
    service.previewHIT(defaultHITInput,htmlQuestion);

    fail("Expected ValidationException when previewing HIT with invalid external question." );
  }
  catch (ValidationException e) {
    // Expected exception
  }
}

public void testValidateInvalidHTMLQuestion() throws Exception {
  // HTMLQuestion has invalid FrameHeight
  try {
    QAPValidator.validateFile(defaultInvalidHTMLQuestionFileName);
    fail("Expected ValidationException when previewing a HIT with an invalid HTMLQuestion");
  } catch (ValidationException e) {
    // Expected exception
    assertContains("ValidationFailure was not caused by an invalid frame height.",e.getMessage());
  }
}

public void testCreateInvalidFormattedContentHIT() throws Exception {
  HITQuestion htmlQuestion = new HITQuestion(defaultInvalidFormattedContentQuestionFileName);

  try {
    service.previewHIT(defaultHITInput,htmlQuestion);

    fail("Expected ValidationException when creating HIT with invalid formatted content." );
  }
  catch (ValidationException e) {
    // Expected exception
  }
}

public void testCreateScriptFormattedContentHIT() throws Exception {
  HITQuestion htmlQuestion = new HITQuestion(defaultScriptFormattedContentQuestionFileName);

  try {
    service.previewHIT(defaultHITInput,htmlQuestion);

    fail("Expected ValidationException when creating HIT with script in formatted content." );
  }
  catch (ValidationException e) {
    // Expected exception
  }
}

public static void validate(String question) throws ValidationException,IOException {
  validate(question,false,QUESTION_FORM_XSD,false);
}

public static void validateFile(String fileName)
  throws ValidationException,IOException {
  validate(fileName,true,false);
}

public static void validate(String question) throws ValidationException,false);
}

public static void validateFile(String fileName)
  throws ValidationException,false);
}