运行 linq 查询时 DbContext 超时

Question

我有以下异步方法查询数据库中的一些数据。

private async Task<List<MyObject>> GetTotalConcert(DateTime d1, DateTime d2, string[] name)
        {
            using (RegistrationDbContext context = new RegistrationDbContext())
            {
                IQueryable<MyObject> results;

                results = (from t1 in context.Table1
                           join t2 in context.Table2 on t1.Id equals t2.Id
                           where (t2.CreatedOn >= d1 && t2.CreatedOn < d2)
                           && (name.Contains(t2.Name))
                           && t1.EventName.Equals("Concert")
                           select new MyObject
                           {
                               Id = t2.Id,
                               EventName = t1.EventName,
                               Status = t2.Status,
                               ProjectName = t2.Name
                           });

                return await results.Distinct().ToAsyncEnumerable().ToList();
            }
        }

此代码在日期范围太宽的情况下失败并出现超时异常。我试图通过这样做来增加超时：

public class RegistrationDbContext : DbContext
    {
        protected override void OnModelCreating(ModelBuilder builder)
        {
            base.OnModelCreating(builder);

            base.Database.SetCommandTimeout(300);

        }
        // Some more code here....
    }

我这里有什么地方做错了吗？如果我运行对数据库本身的 SQL 查询，对于相同的日期范围，它需要将近 18 秒...

我正在使用 ASP.NET 5 MVC6 和 EF7。

对于这些时间范围太宽并且数据库需要更多时间 return 数据的情况，我如何摆脱超时异常？

Answer 1

这个问题很可能与所谓的 Parameter Sniffing Problem, similar to 有关。

您可以从 link:

获取助手 class 的修改版本

using System;
using System.Linq;
using System.Linq.Expressions;

public static class QueryableUtils
{
    public static IQueryable<T> WhereIn<T>(this IQueryable<T> source, Expression<Func<T, DateTime>> dateSelector, DateTime startDate, DateTime endDate)
    {
        var startCond = Expression.GreaterThanOrEqual(dateSelector.Body, Expression.Constant(startDate));
        var endCond = Expression.LessThan(dateSelector.Body, Expression.Constant(endDate));
        var predicate = Expression.Lambda<Func<T, bool>>(Expression.AndAlso(startCond, endCond), dateSelector.Parameters[0]);
        return source.Where(predicate);
    }

    public static IQueryable<T> WhereIn<T>(this IQueryable<T> source, Expression<Func<T, DateTime?>> dateSelector, DateTime startDate, DateTime endDate)
    {
        var startCond = Expression.GreaterThanOrEqual(dateSelector.Body, Expression.Constant(startDate, typeof(DateTime?)));
        var endCond = Expression.LessThan(dateSelector.Body, Expression.Constant(endDate, typeof(DateTime?)));
        var predicate = Expression.Lambda<Func<T, bool>>(Expression.AndAlso(startCond, endCond), dateSelector.Parameters[0]);
        return source.Where(predicate);
    }
}

然后将您的查询更改为：

results = (from t1 in context.Table1
           join t2 in context.Table2.WhereIn(x => x.CreatedOn, d1, d2) on t1.Id equals t2.Id
           where (name.Contains(t2.Name))
           && t1.EventName.Equals("Concert")
           select new MyObject
           {
               Id = t2.Id,
               EventName = t1.EventName,
               Status = t2.Status,
               ProjectName = t2.Name
           });

看看是否有帮助。

运行 linq 查询时 DbContext 超时

DbContext timeout while running linq query

c#

linq

entity-framework

entity-framework-core

asp.net5