LINQ实战

最新推荐文章于 2025-05-02 14:34:03 发布

donghaima

最新推荐文章于 2025-05-02 14:34:03 发布

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分类专栏：基础文章标签： linq query numbers equals string apple

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本文介绍LINQ的基本操作，包括求和、查找最小值、筛选特定元素等，并展示了如何使用LINQ进行数据处理任务，如数组合并、去除重复项、数据库记录的修改与插入等。

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简单合计
int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
double numSum = numbers.Sum();

合计数组中的字符数
string[] words = { "cherry", "apple", "blueberry" };
double totalChars = words.Sum(w => w.Length);

找到最小的值
int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
int minNum = numbers.Min();

找到字符数最少的那个串
string[] words = { "cherry", "apple", "blueberry" };
int shortestWord = words.Min(w => w.Length);

检查数组中是否有至少一个包含ei的值
string[] words = { "believe", "relief", "receipt", "field" };
bool iAfterE = words.Any(w => w.Contains("ei"));

取表中Name字段唯一值并且排序
DataTable orders = dataSet.Tables[0];
EnumerableRowCollection<DataRow> query =(from order in orders.AsEnumerable() orderby order.Field<string>("Name") select order.Field<string>("Name")).Distinct();
DataView view = query.AsDataView();
GridView1.DataSource=view;
GridView1.DataBind();

按表中Name字段分组，合计Money
DataTable orders = dataSet.Tables[0];
var query =from order in orders.AsEnumerable() group order by order.Field<string>("Name") into g select new { Names=g.Key,Moneys=g.Sum(order=>order.Field<decimal>("Money"))};
GridView1.DataSource = query.AsQueryable();
GridView1.DataBind();

内连接
DataTable orders = dataSet.Tables[0];
DataTable citys = dataSet.Tables[1];
var query =from order in orders.AsEnumerable()
           join city in citys.AsEnumerable()
           on order.Field<string>("Name") equals city.Field<string>("Name")
           select new
           {
               Name = order.Field<string>("Name"),
               Money = order.Field<decimal>("Money"),
               City = city.Field<string>("City")
           };

左连接
DataTable orders = dataSet.Tables[0];
DataTable citys = dataSet.Tables[1];
var query =from order in orders.AsEnumerable()
           join city in citys.AsEnumerable()
           on order.Field<string>("Name") equals city.Field<string>("Name") into cits
           select new
           {
               Name = order.Field<string>("Name"),
               Money = order.Field<decimal>("Money"),
               City = cits.Count() > 0 ? cits.First().Field<string>("City") : ""
           };

合并并且取掉重复项
int[] S1 = { 1, 2, 3, 4, 5 };
int[] S2 = { 3, 2, 7, 8, 10 };

var S3s = S1.Union(S2);
foreach (var S3 in S3s)
MessageBox.Show(S3.ToString());

通过新建项LINQ TO SQL类,增加拖拽表TRANSTEST
带事务的修改记录
DataClassesDataContext db = new DataClassesDataContext(ConfigurationManager.ConnectionStrings["TESTDBConnectionString"].ConnectionString);
db.CommandTimeout = 60;
using (TransactionScope ts = new TransactionScope())
{
var records = db.TRANSTEST.Where(p => p.Name == "MAJ'IE");
foreach (var record in records)
{
record.orders = 1;
record.other = DateTime.Now.Second.ToString();
}
db.SubmitChanges();
ts.Complete();
}

增加记录
DataClassesDataContext db = new DataClassesDataContext(ConfigurationManager.ConnectionStrings["TESTDBConnectionString"].ConnectionString);
TRANSTEST record = new TRANSTEST();
record.other = "ILOVEYOU";
db.TRANSTEST.InsertOnSubmit(record);
db.SubmitChanges();