Lambda

Posted 2020-10-04 Lanny Priest

Join:

context.SoftwareModelVersion.Join(context.ModelVersion.Where(m=>m.ModelName==toolStripTextBox1.Text) , q => q.ModelVersoinID, p => p.ModelVersionID, (q, p) => new { SoftwareModelVersionID = q.SoftwareModelVersionID })

 

OrderBy:

var reuslt = group.OrderBy(q=>q.Attribute);

 

var reuslt = group.OrderByDescending(q=>q.Attribute);

 连续排序:

var result = group.OrderByDescending(q=>q.Attribute).ThenBy(q=>q.Attribute2).ThenBy(q=>q.Attribute3);

 

GroupBy:

GroupBy之后通常需要输出具包含统计信息的匿名集合,那么可以这样:

objCollection.GroupBy(q=>q.GroupByKey)

.Select(q=>new {Attribute1 = q.First().GroupByKey, Attribute2 = q.Sum(q.Value));

 

Select,SelectMany:

Select返回集合

SelectMany将序列的每个元素投影到 IEnumerable(T) 并将结果序列合并为一个序列。

class PetOwner

{

    public string Name { get; set; }

    public List<String> Pets { get; set; }

}

 

PetOwner[] petOwners =

{

    new PetOwner { Name="Higa, Sidney",

        Pets = new List<string>{ "Scruffy", "Sam" } },

    new PetOwner { Name="Ashkenazi, Ronen",

        Pets = new List<string>{ "Walker", "Sugar" } },

    new PetOwner { Name="Price, Vernette",

        Pets = new List<string>{ "Scratches", "Diesel" } }

};

 

// Query using SelectMany().

var query1 = petOwners.Select(petOwner => petOwner.Pets).ToList();

//返回List<List<string>>;

var query2 = petOwners.SelectMany(petOwner => petOwner.Pets).ToList();

//返回合并后的List<string>;

MSDN

 

where:

var reuslt = group.Where(q=>q.Attribute.Equal(compareObject));

 

Aggregate:

string[] stra = new string[] { "Able", "was", "I", "ere", "I", "saw", "Elba"};

string aa = stra.Aggregate("",(a, n) => a + " " + n);

输出：

"Able was I ere I saw Elba"