C # improve the knowledge of ADO. NET Object Data Model

OleDbConnection, OracleConnection, or SqlConnection directly executes SQL statements. The current method of connecting to execute SQL statements is quite different. Next let's take a look at the simple addition, deletion, modification, and query operations for a single table, and then look at multi-Table Association queries and parameter queries.
1. add, delete, modify, and query a single table using ADO. NET Entity
There is a table that is an entity user in the project. For test convenience, all fields are of the string type.

1. Add new records
Add a record as follows:

[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. Delete content

[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. Modified content

[Csharp]
Using (OracleEntities entities = new OracleEntities ())
{
User user = entities. User. First <User> (a => a. User. Equals ("id "));
 
User. Remarks = "modified content ";
 
Entities. SaveChanges ();
}

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

User. Remarks = "modified content ";

Entities. SaveChanges ();
} 4. query content
(1) Direct object query

[Csharp]
Using (OracleEntities entities = new OracleEntities ())
{
ObjectQuery <User> result = entities. User; // query all
 
Foreach (User item in result)
{
 
}
}

Using (OracleEntities entities = new OracleEntities ())
{
ObjectQuery <User> result = entities. User; // query all

Foreach (User item in result)
{

}
} (2) Esql Query
ObjectQuery <DbDataRecord> result = entities. CreateQuery <DbDataRecord> ("select value it from OracleEntities. User as it ");
(3) query by conditions
Var result = entities. User. Where (o => o. id. Equals ("id "));
2. join query
For example, another table Other is associated with the User foreign key.

The query is as follows:

[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.2cto.com

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

Foreach (DbDataRecord r in query)
{
String ss = r ["detail"]. ToString ();
}
} Of course, these are the most basic usage, because the usage of Linq and ESql is described in detail later in the usage of Linq and ESql.