C＃筛选器列表中删除任何双宾语 [英] C# Filter List to remove any double object

问题描述

已搜查蚂蚁在这个论坛上测试了许多例子，但不能得到完全的工作方法。

Have searched ant tested many examples in this forum but can't get a fully working method.

我使用LINQ to批量插入实体类的列表（ RemoteReadings）。

I am using linq to bulk insert a list of entity classes (RemoteReadings).

由于唯一约束我需要过滤掉已经插入任何项目。

Due to unique constraints I need to filter out any items already inserted.

Uniqiuness由2列meterid和RemoteReadings表日期时间。

Uniqiuness is composed of 2 columns meterid and datetime in RemoteReadings table.

// approx 5000 records (I need to do this in batches of 2000 due to a 
// constraint in L2S,but can do this after get this working)
List<RemoteReading> lst = createListFromCSV(); 

// Option 1:
// This does not work as am comparing memory list to db list. I need to use contains() method.
// Actually am trying to accomplish this infollowing examples.

List<RemoteReading> myLst = (from ri in db.RemoteReadings                                                       
                            from l in lst 
                            where l.meterid = ri.meterid 
                            && l.date = r.date
                            select ri).ToList();
////

// Option2:
// Get the list from DB that are in memory lst 
List<RemoteReading> myLst = (from ri in db.RemoteReadings                                                       
                            where 
                            // where in this list by comparing meaterid and datemeaured
                            (from l in lst
                            select 
/// help here !
///
                            select ri).ToList<RemoteInterconnectorReading>();


// Option3:
// Get the list from lst that are not in database
// I am bit confused here !


// Tried also to remove from list any duplicates:

List<RemoteReading> result = List<RemoteReading>)myLst.Except(lst).ToList<RemoteReading>();


// Ultimately
db.RemoteReading.InsertAllOnSubmit(result);
db.submitChanges();

任何帮助吗？

Any help please?

推荐答案

由于EF限制，我们无法与内存中的列表加入DB查询。此外，包含只能用原始的列表中使用。所以我们需要做一些努力，找到两列的重复

Due to limitations in EF, we can't join DB query with in-memory list. Also, Contains can only be used with primitive list. So we need to make some efforts to find the duplicates on two columns.

var newItems = createListFromCSV();
var meterIds = newItems.Select(n=> n.meterid).Distinct().ToList();
var dates = newItems.Select(n=> n.date).Distinct().ToList();

var probableMatches = (from ri in db.RemoteReadings                              
                      where (meterIds.Contains(ri.meterids)
                      || dates.Contains(ri.date)
                      select new {ri.merterid, ri.date}).ToList();

var duplicates = (from existingRi in probaleMatches
                 join newRi in newItems
                 on new {existingRi.meterid, existingRi.date}
                 equals {newRi.meterid, newRi.date}
                 select newRi).ToList();

var insertList = newItems.Except(duplicates).ToList();

db.RemoteReadings.Insert(insertList); // or whatever

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