EntityFramework 学习 一 DBEntityEntry

DbEntityEntry是一个重要的类，用来获取各种各样的实体信息

可以通过DBContext的Entry方法获取DbEntityEntry的实例

DBEntityEntry studentEntry = dbcontext.Entry(StudentEntity);

通过DBEntityEntry，可以获取实体的状态，所有属性的当前值和原始值

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

    //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);
    }

}
    

DbEntityEntry可以设置实体的状态如Added、Modified或Deleted

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

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();