通过 LINQ 从实体中获取最后 N 个元素

Question

I want to find the last primary id of a table. Table Name: table1 columns: Id, name, age

var id = _db.table1.OrderByDescending(x => x.Id).FirstOrDefault().Id

The above query is causing performance problem when records exceed 100 000 records. How to improve the performance?

Answer 1

假设 _db.Table1 是可查询的，您可以尝试以下操作：

var id = _db.table1.Max(e => e.Id);

Answer 2

If performance is an issue you could issue a raw query against the database:

int id = _db.table1.SqlQuery<int>("SELECT MAX([Id]) FROM dbo.table1").FirstOrDefault<int>();

Entity Framework Raw SQL Queries: https://msdn.microsoft.com/en-us/library/jj592907%28v=vs.113%29.aspx

It doesn't get any faster than this as far as the selection of data is concerned.