Linq在c＃中查詢數據集？

我有數據集包含兩個表是這樣的：Linq在c＃中查詢數據集？

DataTable dtFields = new DataTable("tmpFieldTable"); 

dtFields.Columns.Add("FieldID"); 
dtFields.Columns.Add("CDGroupID"); 
dtFields.Columns.Add("CDCaption"); 
dtFields.Columns.Add("fldIndex"); 

DataTable dtCDGroup = new DataTable("tmpCDGroup"); 

dtCDGroup.Columns.Add("CDGroupID"); 
dtCDGroup.Columns.Add("Name"); 
dtCDGroup.Columns.Add("Priority"); 

DataSet ds = new DataSet("tmpFieldSet"); 

ds.Tables.Add(dtFields); 
ds.Tables.Add(dtCDGroup);

我如何寫下面的SQL查詢來LINQ

queryString = "Select FieldID, tmpCDGroup.Name, CDCaption, IIF(ISNULL(Priority),99,Priority), fldIndex from tmpFieldList LEFT OUTER JOIN tmpCDGroup ON tmpFieldList.CDGroupID = tmpCDGroup.CDGroupID order by 4,5 ";

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2012-04-17 NIlesh Lanke

我不知道爲什麼你訂購的「4,5 」，但它會是這樣：

var resultArray = tmpFieldList.Join(
    tmpCDGroup,       // inner join collection 
    fieldList => fieldList.CDGroupID,  // outer key selector 
    cd => cd.CDGroupID,     // inner key selector 
    (fieldList, cd) => new {    // result selector 
     FieldID = fieldList.FieldID, 
     Name = cd.Name, 
     CDCaption = cd.CDCaption, 
     Priority = fieldList.Priority ?? 99, 
     fldIndex = fieldList.fldIndex 
    }) 
.OrderBy(result => result.Priority) 
.ThenBy(result => result.fldIndex) 
.ToArray();

然後你就可以訪問使用，例如，

resultArray[0].FieldID

等

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2012-04-17 07:32:41 McGarnagle

因爲我是新的LINQ，請告訴我如何從上面的提示中提取結果？ – 2012-04-17 07:37:44

@NIleshLanke我更新了答案，希望有所幫助。它只是一個具有「FieldID」，「Name」等屬性的匿名類型的數組。 – McGarnagle 2012-04-17 07:43:06

@NellshLanke：看看[Linq 101]（http://code.msdn.microsoft.com/101-LINQ-Samples-3fb9811b）。有很多很好的例子可以開始使用LINQ。 – raznagul 2012-04-17 07:47:18

這可能工作或至少有助於使它工作。請注意，我更改了某些列的類型。

var result = from field in dtFields.AsEnumerable() 
      join cdGroup in dtCDGroup.AsEnumerable() 
      on field.Field<int>("CDGroupID") equals cdGroup.Field<int>("CDGroupID") 
        into fieldGroup 
      from row in fieldGroup.DefaultIfEmpty() 
      let priority = row.IsNull("Priority") ? 99 : row.Field<int>("Priority") 
      orderby priority, row.Field<int>("fldIndex") 
      select new 
      { 
       FieldID = row.Field<int>("FieldID"), 
       GroupName = row.Field<int>("Name"), 
       CDCaption = row.Field<int>("CDCaption"), 
       Priority = priority, 
       fldIndex = row.Field<int>("fldIndex") 
      };

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2012-04-17 07:57:04

Linq在c＃中查詢數據集？

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