Question

我正在努力解决如何有效地构建LINQ查询，以便最大程度地减少对数据库的往返调用次数。

使用下面的当前代码，这些对象创建中的每一个都可以产生大量的打开和关闭数据库连接。

如何重构某些代码以最小化对数据库的调用，并在单个调用中插入更多对象？

我还多次调用SaveChanges，在保存更改之前对上下文中不存在的对象进行处理。

public IActionResult AddSnapshots([FromBody]List<MembershipSnapshot> snapshots, bool? update = false)
        {
            if (!ModelState.IsValid) { return new BadRequestObjectResult(ModelState); }
            if (snapshots.Count == 0)
            {
                ModelState.AddModelError("Empty", "There were no records provided to be inserted.");
                return new BadRequestObjectResult(ModelState);
            }

            // Get the composite keys from the supplied list
            var snapshotKeys = snapshots.Select(s => new { s.MembershipYear, s.DataDate, s.Aggregate }).ToArray();
            // Find which records already exist in the database, pulling their composite keys
            var snapshotsInDb = platformContext.MembershipSnapshots.Where(s => snapshotKeys.Contains(new { s.MembershipYear, s.DataDate, s.Aggregate }))
                                               .Select(s => new { s.MembershipYear, s.DataDate, s.Aggregate }).ToArray();
            // And filter them out, so we remain with the ones that don't yet exist
            var addSnapshots = snapshots.Where(s => !snapshotsInDb.Contains(new { s.MembershipYear, s.DataDate, s.Aggregate }))
                .ToList();
            platformContext.MembershipSnapshots.AddRange(addSnapshots);
            platformContext.SaveChanges();

            // In addition to adding all of the snapshots that didn't exist, we'll populate the
            // membership categories, aggregates and aggregate collections if they don't already exist
            var aggregates = snapshots.Select(s => new { Name = s.Aggregate, Category = s.AggregateCategory }).Distinct();

            var addAggregates = aggregates.Where(a => !platformContext.MembershipAggregates.Any(ma => ma.Name == a.Name))
                                          .GroupBy(a => a.Name).Select(g => g.First())
                                          .Select(a => new Aggregate { Name = a.Name });
            platformContext.AddRange(addAggregates);
            platformContext.SaveChanges();

            var addCategories = aggregates.Where(a => !platformContext.MembershipCategories.Any(c => c.Name == a.Category))
                                          .GroupBy(a => a.Category).Select(g => g.First())
                                          .Select(a => new Category { Name = a.Category });
            platformContext.AddRange(addCategories);
            platformContext.SaveChanges();

            var addAggregateCollection = aggregates.Where(a => !platformContext.AggregateCollections.Any(ma => ma.Name == a.Name))
                                                   .GroupBy(a => a.Name).Select(g => g.First())
                                                   .Select(a => new AggregateCollection()
                                                   {
                                                       Name = a.Name,
                                                       Category = platformContext.MembershipCategories.Where(c => c.Name == a.Category).Single(),
                                                       Description = a.Name,
                                                       AggregateCollectionAggregates = new List<AggregateCollectionAggregate>()
                                                       {
                                                           new AggregateCollectionAggregate()
                                                           {
                                                               Aggregate = platformContext.MembershipAggregates.Where(ma => ma.Name == a.Name).Single()
                                                           }
                                                       }
                                                   });
            platformContext.AddRange(addAggregateCollection);
            platformContext.SaveChanges();

            return new StatusCodeResult(StatusCodes.Status200OK);
        }

Answer 1

Mate，你需要DbContext喜欢餐馆里的服务员。

如果你在一家餐馆和10个朋友在一起，服务员不会接受第一个朋友的订单，然后到厨房提供信息男人做饭，然后来回到第二个朋友再去直到厨房...... （如果这样做，请去另一家餐馆）。

服务员来到你的桌子并获得他需要的所有信息，然后去找男人做饭， 与DbContext相同，你可以添加尽可能多的新对象如你所愿，它会知道每个新对象，只要你初始化对象就不会抱怨。

和服务员一样，如果是一个好的服务员会知道他们有什么酒以及他能给你什么，如果你要求一些其他的葡萄酒，他可以从头开始告诉你＃34;不，我们没有＆＃34 34;因为他是一个很好的服务员，总是知道他有什么。为了使您的Dbcontext变得更好Dbcontext，您需要告诉她每个对象在那里期待什么。

离。初始化

 public class Lunch
    {
        public IEnumerable<Meat> Meat { get; set; } = new List<Meat>();
        public Desert Desert { get; set; } = new Desert();
        public DateTime DateTime { get; set; } = DateTime.Now;
        public bool WaiterIsFriendly { get; set; } = true;
    }

希望你不知道如何使用DbContext !!!

编辑：

如果我的DbContext中有一个名为Lunch的实体，我可以执行以下操作：

  var lunch1=new Lunch();
Context.Lunch.Add(lunch1);
    lunch1.Desert=new Desert();
    lunch1.Meat.add(new Meat());

    var lunch2=new Lunch();
Context.Lunch.Add(lunch2);
    lunch2.Desert=new Desert();
    lunch2.Meat.add(new Meat());

最后我可以说Context.SaveChanges（）;

只有在午餐课上初始化Desert，Meat ......时才会发生这一切。

需要更有效的方法来创建许多实体

1 个答案: