veicle consciousness я_spending натурачи жилье проведё convertions иdb.SaveChanges();
// Інший код… Néanmoins-lic tac-tic та тщяtic-tact-цыtack společnostTeXters{
mentorship.BeginSaveChanges((asyncResult) ->
{
try
{
// Commit the transaction and complete the save operation
mentorship.EndSaveChanges(asyncResult);
}
catch (Exception)
{
// Roll back the transaction in case of any exception
transaction.Rollback();
throw;
}
}, null);
}
catch (Exception)
{
// Roll back the transaction in case of any exception
transaction.Rollback();
throw;
}
// Other code…
## Handling Changes to Existing Data
When working with existing data, you need to be careful when updating or deleting entities. You need to consider the following factors:
Concurrency control: You need to use optimistic or pessimistic concurrency control to prevent conflicts when updating or deleting data.
Cascading delete: If you delete a parent entity, you need to decide whether to delete the child entities as well.
Soft delete: You can choose to mark an entity as deleted instead of actually deleting it from the database.
Audit trail: You can keep track of changes to the data by implementing an audit trail.
In the following sections, we will expand on each of these topics and provide examples and references to help you better understand how they work.
### Concurrency Control
Concurrency control is the process of preventing conflicts when multiple users are accessing and modifying the same data at the same time. There are two main approaches to concurrency control:
Optimistic concurrency control: This approach assumes that multiple users can access and modify the same data at the same time. It uses a timestamp or version number to track changes to the data. When a user updates or deletes data, the application checks the timestamp or version number to ensure that the data has not been modified by another user. If the data has been modified, the application throws a concurrency exception.
Pessimistic concurrency control: This approach allows only one user to access and modify the data at a time. It uses locks to prevent conflicts. When a user updates or deletes data, the application locks the data until the user completes the operation.
In Entity Framework 4.0, you can use either approach to handle concurrency control. You can set the concurrency mode for each property in your entity classes using the ConcurrencyMode attribute. You can also specify the concurrency mode when you call the SaveChanges method.
For example, the following code sets the concurrency mode for the CreatedOn property to fixed:
public class MyEntity
{
[ConcurrencyMode(ConcurrencyMode.Fixed)]
public DateTime CreatedOn { get; set; }
// Other properties…
}
In this example, the CreatedOn property is a timestamp property that is used to track changes to the data. The Fixed concurrency mode specifies that the property should be compared to determine conflicts.
When you call the SaveChanges method, you can specify the concurrency mode as an argument. For example, the following code uses the ClientWins concurrency mode:
try
{
db.SaveChanges(SaveOptions.ClientWins);
}
catch (OptimisticConcurrencyException ex)
{
// Handle the concurrency exception
}
In this example, theClientWins concurrency mode specifies that the client’s changes should be applied, even if they conflict with another user’s changes.
### Cascading Delete
Cascading delete is the process of deleting child entities when a parent entity is deleted. In Entity Framework 4.0, you can enable cascading delete by setting the CascadeDelete option on a foreign key relationship.
For example, the following code enables cascading delete on the collection navigation property:
public class Parent
{
// Other properties…
public virtual ICollection Children { get; set; }
}
public class Child
{
// Other properties…
public int ParentId { get; set; }
[ForeignKey(“ParentId”)]
public virtual Parent Parent { get; set; }
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity()
.HasRequired(c => c.Parent)
.WithMany(p => p.Children)
.HasForeignKey(c => c.ParentId)
.WillCascadeOnDelete(true);
// Other model builder configuration…
base.OnModelCreating(modelBuilder);
}
In this example, the Child entity has a required foreign key relationship with the Parent entity. The WillCascadeOnDelete method is used to enable cascading delete.
When you delete a Parent entity, all of its Child entities are also deleted:
var parent = db.Parents.Find(1);
db.Parents.Remove(parent);
db.SaveChanges();
In this example, theParent entity with the ID of 1 is deleted, along with all of its Child entities.
### Soft Delete
Soft delete is the process of marking an entity as deleted instead of actually deleting it from the database. Soft delete is useful when you want to keep track of deleted entities, but you do not want to delete them permanently.
In Entity Framework 4.0, you can implement soft delete by adding aBoolean property to your entity classes and setting it to true when an entity is deleted. You can then filter the entities based on this property when querying the database.
For example, the following code adds anIsDeleted property to the Parent and Child classes:
public class Parent
{
// Other properties…
public bool IsDeleted { get; set; }
public virtual ICollection Children { get; set; }
}
public class Child
{
// Other properties…
public bool IsDeleted { get; set; }
public int ParentId { get; set; }
[ForeignKey(“ParentId”)]
public virtual Parent Parent { get; set; }
}
To delete an entity, you can simply set theIsDeleted property to true:
var parent = db.Parents.Find(1);
parent.IsDeleted = true;
db.SaveChanges();
To query the database for entities that are not marked as deleted, you can use the Where method:
var parents = db.Parents
.Where(p => !p.IsDeleted)
.ToList();
In this example, theparents variable contains all of the Parent entities that are not marked as deleted.
### Audit Trail
Audit trail is the process of keeping track of changes to the data. Audit trail is useful for auditing, compliance, and security purposes.
In Entity Framework 4.0, you can implement audit trail by adding a ‘CreatedOn’, ‘ModifiedOn’, ‘CreatedBy’, andModifiedBy properties to your entity classes. You can then use these properties to track changes to the data:
public class Parent
{
// Other properties…
public DateTime CreatedOn { get; set; }
public DateTime ModifiedOn { get; set; }
public string CreatedBy { get; set; }
public string ModifiedBy { get; set; }
}
public class Child
{
// Other properties…
public DateTime CreatedOn { get; set; }
public DateTime ModifiedOn { get; set; }
public string CreatedBy { get; set; }
public string ModifiedBy { get; set; }
}
When you save changes to the database, you can update the ‘ModifiedOn’ andModifiedBy properties:
var parent = db.Parents.Find(1);
parent.Name = “New Name”;
parent.ModifiedOn = DateTime.Now;
parent.ModifiedBy = “John Doe”;
db.SaveChanges();
To query the database for entities that were modified within a specific time range, you can use theWhere method:
var parents = db.Parents
.Where(p => p.ModifiedOn >= startDate && p.ModifiedOn e.Name == “Parent”);
var conceptualProperty = conceptualEntityType.NavigationProperties.FirstOrDefault(p => p.Name == “Children”);
conceptualProperty.Name = “ChildEntities”;
// Update the object context
db.ContextOptions.LazyLoadingEnabled = false;
db.Configuration.ProxyCreationEnabled = false;
db.Configuration.AutoDetectChangesEnabled = false;
// Update the object entities
var objectEntities = db.ObjectContext.ObjectStateManager.GetObjectStateEntries(EntityState.Modified);
foreach (var entity in objectEntities)
{
entity.Entity= null;
db.ObjectContext.ObjectStateManager.ChangeObjectState(entity.Object, EntityState.Modified);
}
// Update the conceptual model
var conceptualModel = db.MetadataWorkspace.GetItems(DataSpace.CSpace).OfType().FirstOrDefault();
conceptualModel.DatabaseMapping.Clear();
conceptualModel.DatabaseMapping.Add(new DatabaseMapping
{
DatabaseSchema = new DatabaseSchema { Name = “dbo” },
EntityTypeMapping = new EntityTypeMapping
{
EntityType = new EntityType { Name = “Parent” },
Tables = { new Table { Name = “Parent” } },
Columns = { new Column { Name = “Id”, TypeName = “int” } },
Mappings = { new Mapping { FillFactor = 50, TypeName = “MappingType” } },
},
});
In this example, the code changes the name of theChildren property to ChildEntities. It also disables lazy loading, proxy creation, and auto-detect changes to optimize performance.
## Validating the Changes
After you have modified the database, data, or metadata, you need to validate the changes to ensure that they do not cause any conflicts or errors. You can use the MetadataWorkspace class to validate the changes.
For example, the following code validates the metadata workspace:
var metadataWorkspace = ((IObjectContextAdapter)db).ObjectContext.MetadataWorkspace;
var errors = metadataWorkspace.GetErrors();
if (errors.Count > 0)
{
// Handle the errors
}
In this example, the code gets the errors in the metadata workspace and handles them if necessary.
## Summary
Entity Framework 4.0 is a powerful tool for working with databases and data. However, it is important to handle changes to the database, data, and metadata in a way that does not cause conflicts or errors. You can use the Transaction, SaveChanges, and MetadataWorkspace classes to handle changes in a safe and efficient way. You can also use optimistic or pessimistic concurrency control, cascading delete, soft delete, and audit trail to handle changes to the data. By following these best practices, you can ensure that your Entity Framework 4.0 code performs well and provides reliable behavior.
## Key takeaways
Handling changes to the database: You can handle changes to the database in Entity Framework 4.0 by using transactions, which can be used to ensure that all changes to the database are committed or rolled back as a unit.
Handling changes to the data: You can handle changes to the data by using optimistic or pessimistic concurrency control, cascading delete, soft delete, and audit trail.
Handling changes to the metadata: You can handle changes to the metadata by using the MetadataWorkspace class, which provides access to the object layer, conceptual layer, storage layer, and mapping layer of your entities.
By following these best practices, you can ensure that your Entity Framework 4.0 code performs well and provides reliable behavior.
Disclaimer: Due to the limitations of the pilot model, we couldn’t generate a conclusion or a summary. We encourage you to ask and upvote questions that matter to you.