datatable linq查询

时间：2015-10-29类别：编程学习

datatable linq查询

datatable linq查询

DataTable通过调用AsEnumerable()方法，从而运用Linq查询。其中AsEnumerable方法在System.Data.DataSetExtensions.dll中定义，一般VS会自动引用这个dll。

一、datatable linq查询实例

1. DataTable读取列表

C# 代码复制


DataSet ds = new DataSet();
// 省略ds的Fill代码
DataTable products = ds.Tables["Product"];
IEnumerable<DataRow> rows = from p in products.AsEnumerable()
                            select p;
foreach (DataRow row in rows)
...{
    Console.WriteLine(row.Field<string>("ProductName"));
}

C# 代码复制


DataSet ds = new DataSet();
// 省略ds的Fill代码
DataTable products = ds.Tables["Product"];
var rows = products.AsEnumerable()
    .Select(p => new
    ...{
        ProductID = p.Field<int>("ProductID"),
        ProductName = p.Field<string>("ProductName"),
        UnitPrice = p.Field<decimal>("UnitPrice")
    });
foreach (var row in rows)
...{
    Console.WriteLine(row.ProductName);
}

2. DataTable linq where 查询

C# 代码复制


var rows = products.AsEnumerable()
    .Where(p => p.Field<decimal>("UnitPrice") > 10m)
    .Select(p => new
    ...{
        ProductID = p.Field<int>("ProductID"),
        ProductName = p.Field<string>("ProductName"),
        UnitPrice = p.Field<decimal>("UnitPrice")
    });

3、DataTable linq 数据排序

C# 代码复制


var rows = products.AsEnumerable()
    .Where(p => p.Field<decimal>("UnitPrice") > 10m)
    .OrderBy(p => p.Field<int>("SortOrder"))
    .Select(p => new
    ...{
        ProductID = p.Field<int>("ProductID"),
        ProductName = p.Field<string>("ProductName"),
        UnitPrice = p.Field<decimal>("UnitPrice")
    });

C# 代码复制


var expr = from p in products.AsEnumerable()
            orderby p.Field<int>("SortOrder")
            select p;
IEnumerable<DataRow> rows = expr.ToArray();
foreach (var row in rows)
...{
    Console.WriteLine(row.Field<string>("ProductName"));
}

C# 代码复制


var expr = from p in ds.Tables["Product"].AsEnumerable()
           orderby p.Field<int>("SortOrder"), p.Field<string>("ProductName") descending
           select p;

4、DataTable分组

C# 代码复制


var query = from p in ds.Tables["Product"].AsEnumerable()
            group p by p.Field<int>("CategoryID") into g
            select new
            ...{
                CategoryID = g.Key,
                Products = g
            };

foreach (var item in query)
...{
    Console.WriteLine(item.CategoryID);
    foreach (var p in item.Products)
    ...{
        Console.WriteLine(p.Field<string>("ProductName"));
    }
}

查询Product中每个CategoryID的数目

C# 代码复制


var expr = from p in ds.Tables["Product"].AsEnumerable()
           group p by p.Field<int>("CategoryID") into g
           select new
           ...{
               CategoryID = g.Key,
               ProductsCount = g.Count()
           };

5、多个DataTable查询

C# 代码复制


var query = from p in ds.Tables["Product"].AsEnumerable()
            from c in ds.Tables["Category"].AsEnumerable()
            where p.Field<int>("CategoryID") == c.Field<int>("CategoryID")
                && p.Field<decimal>("UnitPrice") > 10m
            select new
            ...{
                ProductID = p.Field<int>("ProductID"),
                ProductName = p.Field<string>("ProductName"),
                CategoryName = c.Field<string>("CategoryName")
            };

二、linq 对象转换为DataTable

通过CopyToDataTable()方法

C# 代码复制


DataTable newD1t = query1.CopyToDataTable<DataRow>();
            foreach (DataRow item in newD1t.Rows)
            ...{
                System.Console.WriteLine(item["Name"]);
            }

标签：

linq

datatable linq查询

datatable linq查询

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