public void OnGet()
{
var student = _context.Student.Single(m => m.Id == 1);
student.Age = 32;
#region 模拟另外一个用户修改了Age
var task = Task.Run(() =>
{
var options = HttpContext.RequestServices.GetService <DbContextOptions <Data.EFCoreDbContext> >();
using (var context = new Data.EFCoreDbContext(options))
{
var student = context.Student.Single(m => m.Id == 1);
student.Age = 23;
context.SaveChanges();
}
});
task.Wait();
#endregion
var(trySave, isSave) = (0, false);
while (!isSave && trySave++ < 3)
{
try
{
_context.SaveChanges();
}
catch (DbUpdateConcurrencyException ex)
{
_logger.LogError(ex, "database update error");
foreach (var entry in ex.Entries)
{
if (entry.Entity is Models.Student)
{
var currentValues = entry.CurrentValues;
var databaseValues = entry.GetDatabaseValues();
foreach (var property in currentValues.Properties)
{
var currentValue = currentValues[property];
var databaseValue = databaseValues[property];
//这里选择保存哪个值，这里简单选择当前（30）保存到数据库，实际可能还需处理，如余额，就需要数据库当前余额 - 当前数值
currentValues[property] = currentValue;
}
// 刷新原始值
entry.OriginalValues.SetValues(databaseValues);
}
}
}
}
}
public void OnGet()
{
var student = _context.Student.Single(m => m.Id == 1);
student.Age = 32;
//模拟另外一个用户修改了Age
var task = Task.Run(() =>
{
var options = HttpContext.RequestServices.GetService <DbContextOptions <Data.EFCoreDbContext> >();
using (var context = new Data.EFCoreDbContext(options))
{
var student = context.Student.Single(m => m.Id == 1);
student.Age = 23;
context.SaveChanges();
}
});
task.Wait();
//到这，另外一个线程已经将Age修改成23
var trySave = 0;
//若并发冲突异常，重试3次
while (trySave++ < 3)
{
if (TrySaveData())
{
break;
}
}
bool TrySaveData()
{
try
{
_context.SaveChanges();
return(true);
}
catch (DbUpdateConcurrencyException ex)
{
_logger.LogError(ex, $"database update concurrency exception : retry: {trySave}");
//3次尝试保存失败，抛出异常等上层处理，不应该吃掉异常，不然返回成功，实际保存没成功
if (trySave >= 3)
{
throw ex;
}
//若冲突不是当前处理的对象，抛出异常等上层处理
if (!ex.Entries.Any(m => m.Entity is Models.Student))
{
throw ex;
}
var entry = ex.Entries.Select(m => m).Single(m => m.Entity is Models.Student);
//获取当前实体值
var currentValues = entry.CurrentValues;
//获取数据库值
var databaseValues = entry.GetDatabaseValues();
//这里获取当前需要修改的字段
var property = currentValues.Properties.FirstOrDefault(m => m.Name == nameof(student.Age));
var currentValue = currentValues[property];
var databaseValue = databaseValues[property];
//这里赋值多个选择方案，1. 使用当前值 2. 使用数据库值 3. 处理后的值（例如余额，数据库余额 - 当前余额 & 大于0)
currentValues[property] = currentValue;
// 刷新原始值，这里原始值是做并发检查
entry.OriginalValues.SetValues(databaseValues);
return(false);
}
}
}
public IndexModel(ILogger <IndexModel> logger, Data.EFCoreDbContext context)
{
_logger = logger;
_context = context;
}