. Net EF framework-added, deleted, modified, and queried. netef

. Net EF framework-added, deleted, modified, and queried. netef

Declare an EF context object

Model dbContext = new Model ();

Add operation (insert a data entry to the table)

// Declare the object Contact = new contact () for a table; // Add data Contact to the field in the table. name = "James"; contact. enrollmentDate = DateTime. now; // insert dbContext. contacts. add (contact); // save dbContext. saveChanges ();

Modify (modify table data by ID)

// Declare the object Contact of a table = new contact (); Contact. name = "Zhang sansan"; contact. enrollmentDate = DateTime. now; contact. ID = 3; // This field is required for modification or deletion. // modify dbContext. entry <Contact> (contact ). state = System. data. entity. entityState. modified; // save dbContext. saveChanges ();

Delete (delete table data by ID)

// Delete a piece of data with ID 3 Contact = dbContext. Contacts. Find (3); dbContext. Contacts. Remove (contact); dbContext. SaveChanges ();

Query operations (query all data in a table)

 List<Contact> list = dbContext.Contacts.ToList();

Query operation (conditional query)

List <Contact> list = dbContext. Contacts. Where (u => u. Name = "Dongguan"). ToList ();

Query operation (View A single piece of data by ID)

Contact contact = dbContext.Contacts.Find(30);

Create a DbSet object

 public partial class Model : DbContext {     public Model()         : base("name=efdemo")     {     }     public virtual DbSet<Contact> Contacts { get; set; }}

Create a Contact table object

 public class Contact {    public int ID { get; set; }    public string Name { get; set; }    public DateTime EnrollmentDate { get; set; }    public virtual ICollection<Enrollment> Enrollments { get; set; } }