在 ef-core 和 Linq 中获取查询优化答案

【问题标题】：Get Query optimization in ef-core and Linq在 ef-core 和 Linq 中获取查询优化
【发布时间】：2021-09-06 02:03:43
【问题描述】：

这个查询大约需要 5 分钟才能返回 60 条记录。

我可以做些什么来提高性能？

var values = await (from x in _context.things.DefaultIfEmpty()
                      let p = _context.MatchedThings.Where(a => a.Status == Status.Active)
                      .DefaultIfEmpty()
                      .AsNoTracking()
                      select new ThingReport
                      {
                          thing = x,
                          PreferredRate = x.Rate,
                          CreatedDate = x.CreatedDate,
                          IsMatched = (p == null ? false : p.Any(y =>
                          (y.MyThingId == x.Id || y.PairedThingId == x.Id)
                          && (y.MatchedThingStatus == MatchedThingStatus.Matched || y.MatchedThingStatus == MatchedThingStatus.Fulfilled || y.MatchedThingStatus == MatchedThingStatus.Processing
                          || y.MatchedThingStatus == MatchedThingStatus.Completed || y.MatchedThingStatus == MatchedThingStatus.Refunded)
                          )),
                          MatchedOrder = p
                      }).OrderByDescending(a => a.CreatedDate)
                      .ToListAsync();

【问题讨论】：

标签： sql sql-server performance linq entity-framework-core

【解决方案1】：

尝试以下查询。我认为它应该工作得更快，否则您必须分析 SQL 执行计划以查找丢失的索引。

var query =
    from x in _context.things
    from p in _context.MatchedThings
        .Where(p => p.Status == Status.Active)
        .Where(p => (p.MyThingId == x.Id || p.PairedThingId == x.Id)
            && (p.MatchedThingStatus == MatchedThingStatus.Matched || p.MatchedThingStatus == MatchedThingStatus.Fulfilled || p.MatchedThingStatus == MatchedThingStatus.Processing
            || p.MatchedThingStatus == MatchedThingStatus.Completed || p.MatchedThingStatus == MatchedThingStatus.Refunded)
        )
        .Take(1)
        .DefaultIfEmpty()
    select new ThingReport
    {
        thing = x,
        PreferredRate = x.Rate,
        CreatedDate = x.CreatedDate,
        IsMatched = p != null,
        MatchedOrder = p
    };

var result = await query
    .OrderByDescending(a => a.CreatedDate)
    .ToListAsync();

【讨论】：