Entity Framework Tutorial Basics（18）：DBEntityEntry Class

DBEntityEntry Class

DBEntityEntry is an important class, which is useful in retrieving various information about an entity. You can get an instance of DBEntityEntry of a particular entity by using Entry method of DBContext. For example:

DBEntityEntry studentEntry = dbcontext.Entry(StudentEntity);

DBEntityEntry enables you to access entity state, current, and original values of all the property of a given entity. The following example code shows how to retrieve important information of a particular entity.

using (var dbCtx = new SchoolDBEntities())
{
//get student whose StudentId is 1
var student = dbCtx.Students.Find(1);

//edit student name
student.StudentName = "Edited name";

//get DbEntityEntry object for student entity object
var entry = dbCtx.Entry(student);

//get entity information e.g. full name
Console.WriteLine("Entity Name: {0}", entry.Entity.GetType().FullName);

//get current EntityState
Console.WriteLine("Entity State: {0}", entry.State );

Console.WriteLine("********Property Values********");

foreach (var propertyName in entry.CurrentValues.PropertyNames )
{
Console.WriteLine("Property Name: {0}", propertyName);

//get original value
var orgVal = entry.OriginalValues[propertyName];
Console.WriteLine("     Original Value: {0}", orgVal);

//get current values
var curVal = entry.CurrentValues[propertyName];
Console.WriteLine("     Current Value: {0}", curVal);
}

}

Output:
Entity Name: Student
Entity State: Modified
********Property Values********
Property Name: StudentID
Original Value: 1
Current Value: 1
Property Name: StudentName
Original Value: First Student Name
Current Value: Edited name
Property Name: StandardId
Original Value:
Current Value:

DbEntityEntry enables you to set Added, Modified or Deleted EntityState to an entity as shown below.

context.Entry(student).State = System.Data.Entity.EntityState.Modified;

DBEntityEntry class has the following important methods:

Method Name	Return Type	Description
Collection	DBCollectionEntry	Gets an object that represents the collection navigation property from this entity to a collection of related entities. Example: var studentDBEntityEntry = dbContext.Entry(studentEntity); var collectionProperty = studentDBEntityEntry.Collection<course>(s => s.Courses);
ComplexProperty	DBComplexPropertyEntry	Gets an object that represents a complex property of this entity. Example: var studentDBEntityEntry = dbContext.Entry(studentEntity); var complexProperty = studentDBEntityEntry.ComplexProperty(stud.StudentStandard);
GetDatabaseValues	DBPropertyValues	Queries the database for copies of the values of the tracked entity as they currently exist in the database. Changing the values in the returned dictionary will not update the values in the database. If the entity is not found in the database then null is returned. Example: var studentDBEntityEntry = dbContext.Entry(studentEntity); var dbPropValues = studentDBEntityEntry.GetDatabaseValues();
Property	DBPropertyEntry	Gets an object that represents a scalar or complex property of this entity. Example: var studentDBEntityEntry = dbContext.Entry(studentEntity); string propertyName = studentDBEntityEntry.Property("StudentName").Name;
Reference	DBReferenceEntry	Gets an object that represents the reference (i.e. non-collection) navigation property from this entity to another entity. Example: var studentDBEntityEntry = dbContext.Entry(studentEntity); var referenceProperty = studentDBEntityEntry.Reference(s => s.Standard);
Reload	void	Reloads the entity from the database overwriting any property values with values from the database. The entity will be in the Unchanged state after calling this method. Example: var studentDBEntityEntry = dbContext.Entry(studentEntity); studentDBEntityEntry.Reload();

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