EntityFramework 学习 一 DbSet

DBSet类表示一个实体的集合，用来创建、更新、删除、查询操作，DBSet<TEntity>是DBSet的泛型版本

你可以使用DbContext获取DBSet的引用，例如dbContext.Students

 

DBSet中的一些重要方法

 

Method Name	Return Type	Description
Add	Added entity type	Adds the given entity to the context the Added state. When the changes are being saved, the entities in the Added states are inserted into the database. After the changes are saved, the object state changes to Unchanged. Example:  dbcontext.Students.Add(studentEntity)
AsNoTracking<Entity>	DBQuery<Entity>	Returns a new query where the entities returned will not be cached in the DbContext. (Inherited from DbQuery.) Entities returned as AsNoTracking, will not be tracked by DBContext. This will be significant performance boost for read only entities.  Example:  var studentList = dbcontext.Students.AsNoTracking<Student>().ToList<Student>();
Attach(Entity)	Entity which was passed as parameter	Attaches the given entity to the context in the Unchanged state  Example:  dbcontext.Students.Attach(studentEntity);
Create	Entity	Creates a new instance of an entity for the type of this set. This instance is not added or attached to the set. The instance returned will be a proxy if the underlying context is configured to create proxies and the entity type meets the requirements for creating a proxy. Example:  var newStudentEntity = dbcontext.Students.Create();
Find(int)	Entity type	Uses the primary key value to attempt to find an entity tracked by the context. If the entity is not in the context then a query will be executed and evaluated against the data in the data source, and null is returned if the entity is not found in the context or in the data source. Note that the Find also returns entities that have been added to the context but have not yet been saved to the database.  Example:  Student studEntity = dbcontext.Students.Find(1);
Include	DBQuery	Returns the included non generic LINQ to Entities query against a DbContext. (Inherited from DbQuery) Example: var studentList = dbcontext.Students.Include("StudentAddress").ToList<Student>(); var studentList = dbcontext.Students.Include(s => s.StudentAddress).ToList<Student>();
Remove	Removed entity	Marks the given entity as Deleted. When the changes are saved, the entity is deleted from the database. The entity must exist in the context in some other state before this method is called. Example: dbcontext.Students.Remove(studentEntity);
SqlQuery	DBSqlQuery	Creates a raw SQL query that will return entities in this set. By default, the entities returned are tracked by the context; this can be changed by calling AsNoTracking on theDbSqlQuery<TEntity> returned from this method. Example: var studentEntity = dbcontext.Students.SqlQuery("select * from student where studentid = 1").FirstOrDefault<Student>();