C#提高知识 ADO.NET实体数据模型
OleDbConnection，OracleConnection 或者SqlConnection这种连接，直接执行sql语句。现在的连接方式执行sql语句有了很大的不同，下面先看看简单的单表的增删改查操作，然后再看多表的关联查询，带参数查询等。
一、ADO.NET Entity对单表的增删改查
有一个表，即在工程中是一个实体user，为了测试方便，所有字段为string型。
1、增加新记录
增加一条记录如下：
[csharp]
using (OracleEntities entities = new OracleEntities())
{
User uer = User.CreateUser("id", "name", "age", "1");
entities.User.AddObject(user);
entities.SaveChanges();
using (OracleEntities entities = new OracleEntities())
{
User uer = User.CreateUser("id", "name", "age", "1");
entities.User.AddObject(user);
entities.SaveChanges();
}2、删除内容
[csharp]
using (OracleEntities entities = new OracleEntities())
{
User user = entities.User.First<User>(a => a.ID.Equals("id"));
entities.DeleteObject(user);
entities.SaveChanges();
}
using (OracleEntities entities = new OracleEntities())
{
User user = entities.User.First<User>(a => a.ID.Equals("id"));
entities.DeleteObject(user);
entities.SaveChanges();
}3、修改内容
[csharp]
using (OracleEntities entities = new OracleEntities())
{
User user = entities.User.First<User>(a => a.User.Equals("id"));
user.Remarks = "修改了内容";
entities.SaveChanges();
}
using (OracleEntities entities = new OracleEntities())
{
User user = entities.User.First<User>(a => a.User.Equals("id"));
user.Remarks = "修改了内容";
entities.SaveChanges();
}4、查询内容
（1）实体直接查询
[csharp]
using (OracleEntities entities = new OracleEntities())
{
ObjectQuery<User> result = entities.User;//查询所有
foreach (User item in result)
{
}
}
using (OracleEntities entities = new OracleEntities())
{
ObjectQuery<User> result = entities.User;//查询所有
foreach (User item in result)
{
}
}（2）Esql查询
ObjectQuery<DbDataRecord> result = entities.CreateQuery<DbDataRecord>("select value it from OracleEntities.User as it ");
（3）按条件查
var result = entities.User.Where(o => o.id.Equals("id"));
二、关联查询
比如还有个表Other与User外键关联。
进行查询如下：
[csharp]
using (OracleEntities entities = new OracleEntities())
{
string esql = "SELECT b.detail FROM OracleEntities.User as a,OracleEntities.Other as b where a.otherid = b.id and a.id='id'";
ObjectQuery<DbDataRecord> query = entities.CreateQuery<DbDataRecord>(esql);
foreach (DbDataRecord r in query)
{
string ss = r["detail"].ToString();
}
}
using (OracleEntities entities = new OracleEntities())
{
string esql = "SELECT b.detail FROM OracleEntities.User as a,OracleEntities.Other as b where a.otherid = b.id and a.id='id'"; www.zzzyk.com
ObjectQuery<DbDataRecord> query = entities.CreateQuery<DbDataRecord>(esql);
foreach (DbDataRecord r in query)
{
string ss = r["detail"].ToString();
}
} 当然这些都是最基本的用法，因为使用的Linq和ESql，在后面再Linq和ESql的用法里再详细说明。
补充：软件开发 , C# ,
