在 Entity Framework 中修改同一个实体是否会同步将实体保存到数据库中？ 抛出异常？

Question

I'm investigating a bug in our systems and when reviewing the code I saw that the developer queried twice the same entity and saved it with different values.

I simplified the case for example:

Person Data:
id  |   name    |   age |   HasLicence
1   |   david   |   27  |   true


using (DbContext dbContext = new DbContext())
{
    Person person1 = dbContext.Persons.FirstOrDefault(p=>p.age == 27);
    Person person2 = dbContext.Persons.FirstOrDefault(p=>p.name == "david");
    
    person1.HasLicence = false;
    person2.HasLicence = true;
    .
    .
    // more logic..
    .
    .
    dbContext.SaveChanges();
}

Does this will save the entity to the database synchronously? throw exception?

Answer 1

Simple answer is both variables are referencing same object instance(proxy).

So when you update person1.HasLicence same value will be on person2.HasLicence.

a.HasLicence = true;
Assert.AreEqual(a.HasLicence , b.HasLicence );

b.HasLicence = false;
Assert.AreEqual(a.HasLicence , b.HasLicence );

_dataContext.Save(); // updates only one entity

Behavior might be different if you have some changed settings for datacontext.

IF you want to know more how entity frameworks works you can access it on github

https://github.com/dotnet/ef6