ADO.NET實體數據模型詳細介紹

2020-01-24 03:39:25

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OleDbConnection，OracleConnection 或者SqlConnection這種連接，直接執行sql語句?，F在的連接方式執行sql語句有了很大的不同，下面先看看簡單的單表的增刪改查操作，然后再看多表的關聯查詢，帶參數查詢等。
一、ADO.NET Entity對單表的增刪改查
有一個表，即在工程中是一個實體user，為了測試方便，所有字段為string型。

1、增加新記錄
增加一條記錄如下：

[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、刪除內容

復制代碼代碼如下:

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、修改內容

復制代碼代碼如下:

using (OracleEntities entities = new OracleEntities())
{
                User user = entities.User.First<User>(a => a.User.Equals("id"));

                user.Remarks = "修改了內容";

                entities.SaveChanges();
}

using (OracleEntities entities = new OracleEntities())
{
User user = entities.User.First<User>(a => a.User.Equals("id"));

user.Remarks = "修改了內容";

entities.SaveChanges();
}

4、查詢內容
（1）實體直接查詢
[/code]
using (OracleEntities entities = new OracleEntities())
{
                ObjectQuery<User> result = entities.User;//查詢所有

                foreach (User item in result)
                {

                }
}

using (OracleEntities entities = new OracleEntities())
{
ObjectQuery<User> result = entities.User;//查詢所有

foreach (User item in result)
{

}
}
[/code]
（2）Esql查詢

復制代碼代碼如下:

ObjectQuery<DbDataRecord> result = entities.CreateQuery<DbDataRecord>("select value it  from  OracleEntities.User as it ");

（3）按條件查

復制代碼代碼如下:

var result = entities.User.Where(o => o.id.Equals("id"));

二、關聯查詢
比如還有個表Other與User外鍵關聯。

進行查詢如下：

復制代碼代碼如下:

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.49028c.com

ObjectQuery<DbDataRecord> query = entities.CreateQuery<DbDataRecord>(esql);

                foreach (DbDataRecord r in query)
                {
                    string ss = r["detail"].ToString();
                }
}

當然這些都是最基本的用法，因為使用的Linq和ESql，在后面再Linq和ESql的用法里再詳細說明。

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