Linq Query 不断抛出“无法创建 System.Object... 类型的常量值”，为什么？

下面是代码示例:

private void loadCustomer(int custIdToQuery)
{
var dbContext = new SampleDB();
try
{
var customerContext = from t in dbContext.tblCustomers      // keeps throwing:
where t.CustID.Equals(custIdToQuery) // Unable to create a constant value of type 'System.Object'.
select new                           // Only primitive types ('such as Int32, String, and Guid')
{                                    // are supported in this context.
branchId = t.CustomerBranchID,   //
branchName = t.BranchName        //
};                                   //


if (customerContext.ToList().Count() < 1) //Already Tried customerContext.Any()
{
lstbCustomers.DataSource = customerContext;
lstbCustomers.DisplayMember = "branchName";
lstbCustomers.ValueMember = "branchId";
}
else
{
lstbCustomers.Items.Add("There are no branches defined for the selected customer.");
lstbCustomers.Refresh();
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
finally
{
dbContext.Dispose();
}
}

我不能理解我做错了什么。我一直得到 ”无法创建“ System”类型的常数值。反对。在此上下文中只支持基本类型(如 Int32、 String 和 Guid)。”

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最佳答案

Use == instead of Equals:

where t.CustID == custIdToQuery

If the types are incorrect you may find that this doesn't compile.

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I had the same issue when I was trying to do .Equals with a nullable decimal. Using == instead works nicely. I guess this is because it's not trying to match the exact "type" of decimal? to decimal.

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I had the same issue with a nullable int. Using == instead works nicely, but if you want to use .Equals, you can compare it to the value of the nullable variable, so

where t.CustID.Value.Equals(custIdToQuery)
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I was faced the same issue and i was comparing Collection Object "User" with integer data type "userid" (x.User.Equals(userid))

from user in myshop.UserPermissions.Where(x => x.IsDeleted == false && x.User.Equals(userid))

and correct Query is x.UserId.Equals(userid)

from user in myshop.UserPermissions.Where(x => x.IsDeleted == false && x.UserId.Equals(userid))
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In my case, I changed the direct call of (sender as Button).Text to indirect call using a temp var, has worked. working code:

private void onTopAccBtnClick(object sender, EventArgs e)
{
var name = (sender as Button).Text;
accountBindingSource.Position =
accountBindingSource.IndexOf(_dataService.Db.Accounts.First(ac => ac.AccountName == name));
accountBindingSource_CurrentChanged(sender, e);
}

buggy code:

private void onTopAccBtnClick(object sender, EventArgs e)
{
accountBindingSource.Position =
accountBindingSource.IndexOf(_dataService.Db.Accounts.First(ac => ac.AccountName == (sender as Button).Text));
accountBindingSource_CurrentChanged(sender, e);
}

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