Linq 数据库通用的操作类

From:http://oct01.cn/all.aspx?id=14

1. 建一个project 命名为DLinq ，添加一个Linq To SQL 的数据源，这里以经典的Northwind数据库为例，命名为NWDB.dbml 。

2. 建另一个Project 为DAL层 ，添加一个Table工厂， 这样我们就可以通过实体来获得Table

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace DAL
{
public static class TableFactory
{
public static System.Data.Linq.Table<T> CreateTable<T>() where T : class
{
return Database.NWDB.GetTable<T>();
}
}
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace DAL
{
public static class Database
{
private static DLinq.NWDBDataContext _NWDB = null;

public static DLinq.NWDBDataContext NWDB
{
get
{
if (_NWDB == null)
_NWDB = new DLinq.NWDBDataContext();
return _NWDB;
}
}

}
}
3. 借助Linq的特性，现在就可以写通用的数据库操作类了

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace DAL
{
public class Utility
{
public static void Insert<T>(T TEntity) where T : class
{
var table = TableFactory.CreateTable<T>();
table.InsertOnSubmit(TEntity);
}

public static IEnumerable<T> Where<T>(Func<T, bool> predicate) where T : class
{
var table = TableFactory.CreateTable<T>();
return table.Where(predicate).AsEnumerable();
}

public static void SubmitChanges()
{
Database.NWDB.SubmitChanges();
}
}
}

4. 现在让我们来写个测试方法来测试一下是否成功

using System.Collections.Generic;
using System.Linq;
using System.Text;
using DAL;
using DLinq;

namespace DALTest
{
class Program
{
static void Main(string[] args)
{
InsertTest();
WhereTest();
Console.WriteLine("All testings are success!");
Console.Read();
}

private static void InsertTest()
{
Customer _customer=new Customer{
CustomerID="Bruce",
ContactName="Lee",
CompanyName ="CodingSky",
City ="Shenzhen"};
Utility.Insert(_customer);
Utility.SubmitChanges();
}

private static void WhereTest()
{
var _result= Utility.Where<Customer>(c => c.CustomerID == "Bruce");
var _list = _result.ToList();
if (_list.Count == 0)
{
Console.WriteLine("No result!");
return;
}
Console.WriteLine("Query result is:");
_list.ForEach(c => Console.WriteLine(Toolkits.StringExtension.ToString(c)));
}

}
}
5. 其中WhereTest调用了另一个Project的StringExtension类，这个类主要扩展了ToString方法，通过Reflection 来读取实例的所有属性以及它们的值。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Toolkits
{
public class StringExtension
{
public static string ToString<T>(T t) where T:class
{
var typeInfo = BLReflection.GetProperties(typeof(T));

var rType = (from q in typeInfo select new
{
TypeName= q.PropertyType.Name,
PropName= q.Name ,
Value= q.GetValue(t, null)
}).ToList();

StringBuilder sb = new StringBuilder();
string header="Class Name: {0}\n";
sb.AppendFormat(header , typeof(T).Name);
rType.ForEach(c => sb.Append(String.Format ("\t{0}: {1} ({2}),\n", c.PropName, c.Value,c.TypeName) ));
string result=sb.ToString ();
return (result.Length > header.Length ? result.Substring(0, result.Length - 2)+"\n" : header);
}
}
}
6. 最后，输出的结果应该是这样：

Query result is:
Class Name: Customer
CustomerID: Bruce (String),
CompanyName: CodingSky (String),
ContactName: Lee (String),
ContactTitle: (String),
Address: (String),
City: Shenzhen (String),
Region: (String),
PostalCode: (String),
Country: (String),
Phone: (String),
Fax: (String),
Orders: System.Data.Linq.EntitySet`1[DLinq.Order] (EntitySet`1)

All testings are success!

================================================================

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace DAL
{
public class Utility
{
public static void Insert<T>(T TEntity) where T : class
{
var table = TableFactory.CreateTable<T>();
table.InsertOnSubmit(TEntity);
}

public static void Delete<T>(T TEntity) where T : class
{
var table = TableFactory.CreateTable<T>();
table.DeleteOnSubmit(TEntity);
}

public static void Delete<T>(Func<T, bool> predicate) where T : class
{
var table = TableFactory.CreateTable<T>();
var dResult = Where<T>(predicate);
table.DeleteAllOnSubmit(dResult );
}

public static void Update<T>(T TEntity, Action<T> action)
{
action(TEntity);
SubmitChanges();
}

public static void InsertAll<T>(IEnumerable <T> TEntities) where T : class
{
var table = TableFactory.CreateTable<T>();
table.InsertAllOnSubmit( TEntities);
}

public static void DeleteAll<T>(IEnumerable<T> TEntities) where T : class
{
var table = TableFactory.CreateTable<T>();
table.DeleteAllOnSubmit(TEntities);
}

public static IEnumerable<T> SelectAll<T>() where T : class
{
var table = TableFactory.CreateTable<T>();
return table.Select(c => c).AsEnumerable();
}

public static IEnumerable<T> Where<T>(Func<T, bool> predicate) where T : class
{
var table = TableFactory.CreateTable<T>();
return table.Where(predicate).AsEnumerable();
}

public static void SubmitChanges()
{
Database.NWDB.SubmitChanges();
}
}
}

同样的， 我们也是写一些Test 方法来验证一下是否正确

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using DAL;
using DLinq;
using Toolkits;

namespace DALTest
{
class Program
{
static void Main(string[] args)
{
//SelectAllTest();
InsertTest();
WhereTest();
UpdateTest();
WhereTest();
DeleteTest1();
WhereTest();
Console.WriteLine("All testings are success!");
Console.Read();
}

private static void InsertTest()
{
Customer _customer=new Customer{
CustomerID="Bruce",
ContactName="Lee",
CompanyName ="CodingSky",
City ="Shenzhen"};
Utility.Insert(_customer);
Utility.SubmitChanges();
}

private static void DeleteTest1()
{
Utility.Delete<Customer>(c => c.CustomerID == "Bruce");
Utility.SubmitChanges();
}

private static void DeleteTest2()
{
var _result= Utility.Where<Customer>(c => c.CustomerID == "Bruce");
if (_result.Count() > 0)
{
Utility.Delete(_result.First());
Utility.SubmitChanges();
}
}

private static void UpdateTest()
{
var _result= Utility.Where<Customer>(c => c.CustomerID == "Bruce");
if (_result.Count() > 0)
{
var _customer = _result.First();
if (_customer != null)
{
Utility.Update(_customer, c =>
{
c.ContactName = "Jack";
c.CompanyName = "Microsoft";
c.City = "Beijing";
});
Utility.SubmitChanges();
}
}
}

private static void SelectAllTest()
{
var _result = Utility.SelectAll<Customer>();
var _list = _result.ToList();
if (_list.Count == 0)
{
Console.WriteLine("No result!");
return;
}
_list.ForEach(c => Console.WriteLine(StringExtension.ToString(c)));
}

private static void WhereTest()
{
var _result= Utility.Where<Customer>(c => c.CustomerID == "Bruce");
var _list = _result.ToList();
if (_list.Count == 0)
{
Console.WriteLine("No result!");
return;
}
Console.WriteLine("Query result is:");
_list.ForEach(c => Console.WriteLine(StringExtension.ToString(c)));
}

}
}

其他代码（例如TableFactory，StringExtension）请参考上一篇 ：http://blog.csdn.net/fengart/archive/2008/08/19/2798534.aspx

以上的Test是先在Customers表中Insert一个叫Bruce的家伙，接着把他的ContactName修改为Jack ，最后Delete他。

（其中Customers表的数据太多，所以我把SelectAllTest方法注释掉了）

最后打印的结果应该是这样：

Query result is:
Class Name: Customer
CustomerID: Bruce (String),
CompanyName: CodingSky (String),
ContactName: Lee (String),
ContactTitle: (String),
Address: (String),
City: Shenzhen (String),
Region: (String),
PostalCode: (String),
Country: (String),
Phone: (String),
Fax: (String),
Orders: System.Data.Linq.EntitySet`1[DLinq.Order] (EntitySet`1)

Query result is:
Class Name: Customer
CustomerID: Bruce (String),
CompanyName: Microsoft (String),
ContactName: Jack (String),
ContactTitle: (String),
Address: (String),
City: Beijing (String),
Region: (String),
PostalCode: (String),
Country: (String),
Phone: (String),
Fax: (String),
Orders: System.Data.Linq.EntitySet`1[DLinq.Order] (EntitySet`1)

No result!
All testings are success!