Entify框架 - 异步选择与哪里条件(Entify Framework - async select with where condition)

我正在使用ASP.NET Core和Entity Framework。

首先，我选择一个员工，然后选择满足条件的所有员工（为了展示有效的工作）：

var a = db.Employee.FirstOrDefault(); var b = db.Employee.Where(x => x.FirstName == "Jack");

现在我尝试一样，但异步：

var c = await db.Employee.FirstOrDefaultAsync(); var d = await db.Employee.Where(x => x.FirstName == "Jack");

但是，对于“WHERE”，没有异步版本，第二行代码无法编译 - 我收到错误

...不包含GetAwaiter的定义...

在这种情况下，如何在WHERE条件下执行SELECT ？

好的，从答案我看到ToListAsync（）将解析“var d = ...”行。 但是，这个问题仍然存在，我之前并不知道它很重要。 在这种情况下，我只是试图选择一组将被删除的记录，对于在代码中进一步处理数据的目的，我不感兴趣访问数据。 所以我修改了所有4个代码版本，目的是同步或异步删除一个或多个记录。 为什么只有最后一个需要ToListAsync（），实际上不会从数据库中检索记录？

var a = db.Employee.FirstOrDefault(); db.Employee.Remove(a); // db.Employee.RemoveRange(a); <- this also works? db.SaveChanges(); var b = db.Employee.Where(x => x.FirstName == "Jack"); db.Employee.RemoveRange(b); db.SaveChanges(); var c = await db.Employee.FirstOrDefaultAsync(); db.Employee.Remove(c); await db.SaveChangesAsync(); var d = await db.Employee.Where(x => x.FirstName == "Jack").ToListAsync(); db.Employee.RemoveRange(d); await db.SaveChangesAsync();

I'm using ASP.NET Core with Entity Framework.

First I select an employee, and then all employees that satisfy a condition (for the purpose of displaying what works):

var a = db.Employee.FirstOrDefault(); var b = db.Employee.Where(x => x.FirstName == "Jack");

Now I try the same, but asynchronously:

var c = await db.Employee.FirstOrDefaultAsync(); var d = await db.Employee.Where(x => x.FirstName == "Jack");

However, for the "WHERE" there's no async version, and the second line of code doesn't compile - I get an error

... does not contain a definition for GetAwaiter ...

How do I perform a SELECT with a WHERE condition in this case?

OK, from the answers I see that ToListAsync() will resolve the "var d = ..." line. However, there's a continuation to this issue, I wasn't aware before that it matters. In this case I'm just trying to select a set of records that will be deleted, I'm not interested in accessing the data for the purpose of manipulating it further in the code. So I amended all 4 code versions with purpose to delete one or more records, synchronously or asynchronously. Why does only the last one need a ToListAsync(), won't that actually retrieve the records from the database?

var a = db.Employee.FirstOrDefault(); db.Employee.Remove(a); // db.Employee.RemoveRange(a); <- this also works? db.SaveChanges(); var b = db.Employee.Where(x => x.FirstName == "Jack"); db.Employee.RemoveRange(b); db.SaveChanges(); var c = await db.Employee.FirstOrDefaultAsync(); db.Employee.Remove(c); await db.SaveChangesAsync(); var d = await db.Employee.Where(x => x.FirstName == "Jack").ToListAsync(); db.Employee.RemoveRange(d); await db.SaveChangesAsync();

最满意答案

你可以这样做。

如果您需要检索一个对象，则：

var d = await db.Employee.FirstOrDefaultAsync(x => x.FirstName == "Jack");

如果您需要检索列表，则：

var d = await db.Employee.Where(x => x.FirstName == "Jack").ToListAsync();

You can do it like this.

If you need to retrieve one object then :

var d = await db.Employee.FirstOrDefaultAsync(x => x.FirstName == "Jack");

If you need to retrieve list then :

var d = await db.Employee.Where(x => x.FirstName == "Jack").ToListAsync();Entify框架 - 异步选择与哪里条件(Entify Framework - async select with where condition)

我正在使用ASP.NET Core和Entity Framework。

首先，我选择一个员工，然后选择满足条件的所有员工（为了展示有效的工作）：

var a = db.Employee.FirstOrDefault(); var b = db.Employee.Where(x => x.FirstName == "Jack");

现在我尝试一样，但异步：

var c = await db.Employee.FirstOrDefaultAsync(); var d = await db.Employee.Where(x => x.FirstName == "Jack");

但是，对于“WHERE”，没有异步版本，第二行代码无法编译 - 我收到错误

...不包含GetAwaiter的定义...

在这种情况下，如何在WHERE条件下执行SELECT ？

好的，从答案我看到ToListAsync（）将解析“var d = ...”行。 但是，这个问题仍然存在，我之前并不知道它很重要。 在这种情况下，我只是试图选择一组将被删除的记录，对于在代码中进一步处理数据的目的，我不感兴趣访问数据。 所以我修改了所有4个代码版本，目的是同步或异步删除一个或多个记录。 为什么只有最后一个需要ToListAsync（），实际上不会从数据库中检索记录？

var a = db.Employee.FirstOrDefault(); db.Employee.Remove(a); // db.Employee.RemoveRange(a); <- this also works? db.SaveChanges(); var b = db.Employee.Where(x => x.FirstName == "Jack"); db.Employee.RemoveRange(b); db.SaveChanges(); var c = await db.Employee.FirstOrDefaultAsync(); db.Employee.Remove(c); await db.SaveChangesAsync(); var d = await db.Employee.Where(x => x.FirstName == "Jack").ToListAsync(); db.Employee.RemoveRange(d); await db.SaveChangesAsync();

I'm using ASP.NET Core with Entity Framework.

First I select an employee, and then all employees that satisfy a condition (for the purpose of displaying what works):

var a = db.Employee.FirstOrDefault(); var b = db.Employee.Where(x => x.FirstName == "Jack");

Now I try the same, but asynchronously:

var c = await db.Employee.FirstOrDefaultAsync(); var d = await db.Employee.Where(x => x.FirstName == "Jack");

However, for the "WHERE" there's no async version, and the second line of code doesn't compile - I get an error

... does not contain a definition for GetAwaiter ...

How do I perform a SELECT with a WHERE condition in this case?

OK, from the answers I see that ToListAsync() will resolve the "var d = ..." line. However, there's a continuation to this issue, I wasn't aware before that it matters. In this case I'm just trying to select a set of records that will be deleted, I'm not interested in accessing the data for the purpose of manipulating it further in the code. So I amended all 4 code versions with purpose to delete one or more records, synchronously or asynchronously. Why does only the last one need a ToListAsync(), won't that actually retrieve the records from the database?

var a = db.Employee.FirstOrDefault(); db.Employee.Remove(a); // db.Employee.RemoveRange(a); <- this also works? db.SaveChanges(); var b = db.Employee.Where(x => x.FirstName == "Jack"); db.Employee.RemoveRange(b); db.SaveChanges(); var c = await db.Employee.FirstOrDefaultAsync(); db.Employee.Remove(c); await db.SaveChangesAsync(); var d = await db.Employee.Where(x => x.FirstName == "Jack").ToListAsync(); db.Employee.RemoveRange(d); await db.SaveChangesAsync();

最满意答案

你可以这样做。

如果您需要检索一个对象，则：

var d = await db.Employee.FirstOrDefaultAsync(x => x.FirstName == "Jack");

如果您需要检索列表，则：

var d = await db.Employee.Where(x => x.FirstName == "Jack").ToListAsync();

You can do it like this.

If you need to retrieve one object then :

var d = await db.Employee.FirstOrDefaultAsync(x => x.FirstName == "Jack");

If you need to retrieve list then :

var d = await db.Employee.Where(x => x.FirstName == "Jack").ToListAsync();