We Keep Coding

Duplicating Entity Framework entities

I have this EF query:
var records = mydata.Where(a => some condition).ToList();
Records is a list of Record objects. Record is a database table that has a one to many relationship called "relation".
The EF object represents that member variable as Collection<Relation>.
After the where above, I see that "relation" member variable contains a collection of 18 entities.
I need to duplicate those Record objects, so that I am detaching them first, this way:
var detached = this.DetachEntities(records, db, "RecordId");
Where this.DetachEntities is defined this way:
private T DetachEntity<T>(T entity, Repositories.GestionActivosEntities db, string keyName) where T : class
{
db.Entry(entity).State = EntityState.Detached;
if (entity.GetType().GetProperty(keyName) != null)
{
entity.GetType().GetProperty(keyName).SetValue(entity, 0);
}
return entity;
}
private List<T> DetachEntities<T>(List<T> entities, Repositories.GestionActivosEntities db, string keyName) where T : class
{
foreach (var entity in entities)
{
this.DetachEntity(entity, db, keyName);
}
return entities;
}
After I detached the entities, I am doing:
db.Record.AddRange(detached);
The problem, is that, after I detached the list, the relation is not copied also, resulting that "relation" member variable contains no elements.
How can I keep the relation elements after detaching?
EDIT:
This shows the debugging session:
The breakpoint is placed in the line where the query is done. The cursor shows the line after the query was executed.
This screenshot shows the child records ValorCampo and Workflow
This screenshot shows the entity after detaching it. Note the child records are not present in the detached object
As I have told, the problem only is when detaching. Child records are not kept. Database rows remain untouched.

I had the same problem, unfortunately navigation properties are lost after detaching an Item or when entity state is changed to detached.
what you can do is clone the entity
one way to do this is : Context.Entry(your_entity).CurrentValues.ToObject();
however this will not clone the navigation properties either
if you fully want to clone an object among with navigation properties
the easiest way for me to achieve it was using automapper library for c#
Below is a sample usage:
var config = new MapperConfiguration(cfg => cfg.CreateMap<originalObject, T>());
var mapper = new Mapper(config);
// or
var mapper = config.CreateMapper();
T clonedObject = mapper.Map<T>(originalObject);
after you clone and detach the original object, you can add
db.Record.AddRange(clonedObject );
and below is a generic extension to do it
public static object Map<T>(this T source)
{
var fullName = source.GetType().FullName;
var sourceType = source.GetType();
var baseType = ObjectContext.GetObjectType(source.GetType());
var config = new MapperConfiguration(cfg =>
cfg.CreateMap(sourceType, baseType));
var mapper = config.CreateMapper();
var entity = mapper.Map(source, sourceType, baseType);
return entity;
}
where you can call it like
var clonedObject = originalObject.Map();
Hope this helps!

ASP.Net MVC TryUpdateModel() equivalent for using in a Windows Application

TryUpdateModel is one of the methods in System.Web.Mvc,but I need to use it in windows application which does not have this library.
Any similar method in EF or other suggestions so that I can update an entity without matching fields one by one with the target model?

I tried many solutions but finally I wrote my own method via reflection which worked perfect for me as follows:
public void TryUpdateModel<T>(T existingModel, T newModel)
{
PropertyInfo[] properties = existingModel.GetType()
.GetProperties()
.Where(pi => !(pi.PropertyType.IsSubclassOf(typeof(T))))
.ToArray();
foreach (var item in properties)
{
var propName = item.Name;
if (item.PropertyType.IsSealed && item.PropertyType.IsSerializable && item.Name != existingModel.GetType().Name + "Id")
{
var newValue = db.Entry(newModel).Property(propName).CurrentValue;
db.Entry(existingModel).Property(propName).CurrentValue = newValue;
}
}
}
It gets 2 models (as they are generic classes but should be the same) in which first one is the model fetched from database and second one is what submitted from the UI form.
It updates property values from newModel to existingModel except navigation properties and primary key so that entity framework realizes that values are changed and have to be updated.

How can I detect changes to properties in a specific entity in Entity Framework Core 2.x?

When a user saves changes to an object myObject, I'd like to log the fields that were updated to that object.
I can get an object with
var myObject = await context.MyObjects.SingleAsync(x => x.Id == id);
And I see that I can get an IEnumerable<PropertyEntry> with
var changes = context.Entry(myObject).Properties.Where(x => x.IsModified);
But in my changes list I don't see the field name anywhere. Also, it seems to take 2 full seconds to make this members query in LINQPad. That doesn't seem right.
How do I complete the following statement?
Consolse.Write($"The field {what goes here?} was updated from {change.OriginalValue} to {change.CurrentCalue}.");
Other StackOverflow questions I've found are for previous versions of Entity Framework, or override SaveChanges and don't look for specific entities.
Update! Got it.
public string GetChangeLog<T>(
ApplicationDbContext context,
T entity)
{
var sb = new StringBuilder();
var changes = context.Entry(entity).Properties.Where(x => x.IsModified);
foreach (var change in changes)
{
var propertyBase = (IPropertyBase)change.Metadata;
sb.Append($"\"{propertyBase.Name}\" was changed from \"{change.OriginalValue}\" to \"{change.CurrentValue}\"\n");
}
return sb.ToString();
}

Use the .Metadata property to retrieve a IPropertyBase. That will tell you what has actually changed.

EF Repository with UoW Update

I believe this is asked somewhere else but I can't find straight solution.
My Api is passing object model and on the server side every value of that object which is not passed is considered null (makes sense).
Is there way I can tell EF6 not to update entity with null values from passed object in manner I don't have to write each property and check if it's null.
Pseudo code
API
Update(int id, TaskEntity obj)
{
unitOfWork.Tasks.Update(id, userTask);
...
unitOfWork.Save()
}
Repo update
Update(int id, T entity)
{
var existingRecord = Get(id); //Gets entity from db based on passed id
if (existingRecord != null)
{
var attachedEntry = Context.Entry(existingRecord);
attachedEntry.CurrentValues.SetValues(entity);
}
}
My problem is that any data with null values will actually rewrite existing db record value with nulls.
Please point me to a solution or article where this is solved. Should I go reflections, maybe automapper could handle this (it's not its purpose i believe), or some kind of helper method should be written, as my objects can contain sub object.
Thank you in advance.

You can do something like this
Update(int id, T entity,string[] excludedFields)
{
var existingRecord = Get(id); //Gets entity from db based on passed id
if (existingRecord != null)
{
var attachedEntry = Context.Entry(existingRecord);
attachedEntry.CurrentValues.SetValues(entity);
for(var field in excludedFields)
{
attachedEntry.Property(field).IsModified = false;
}
}
}
some scenaries requires you to update part of the object and sometimes other parts, the best way in my opinion is to pass the fields to exclude from the update
hope it will help you

Personally not a big fan of hitting database and doing a get operation before doing an update. May be while doing the ajax call, you can send a list of properties which you should update (so that the scenario where updating to null values (erasing existing ones) will also be handled).
I'm doing small modifications to what #Hadi Hassan has done (without hitting database for getting the entity):
Update(T entity,string[] includedFields)
{
var existingRecord = Context.Attach(entity); // assuming primary key (id) will be there in this entity
var attachedEntry = Context.Entry(existingRecord);
for(var field in includedFields)
{
attachedEntry.Property(field).IsModified = true;
}
}
Note - attachedEntry.Property(field).IsModified will not work for related entities

Finding out actual changes/diff done in database

Is it possible in Entity Framework to figure out the actual changes/diff which entity framework is going to make in the database?
Consider an example, let say that some rows are already present in the database and we try to add them again. Since the rows are already present, the actual changes/diff made in the database is null. Similarly, if I try to 10 rows, out of which only 3 got updated, then I want only those 3.
I was trying using DbContext.ChangeTracker to achieve the same but it looks like that it returns all the rows which we are trying to add/update/delete irrespective of whether some of them are already there in the database. Can someone confirm this behavior as well?

I used the following code in my base repository to get a dictionary of modified property names and the old DB values. The new values can be get easily by the TModel object itself.
private Dictionary<string, object> GetModifiedProperties(TModel model)
{
var entry = Context.Entry(model);
// entry is detached.
// set entry to database entry and its CurrentValues to model values
if (entry.State == EntityState.Detached)
{
object key = model.GetType().GetProperty("Id").GetValue(model);
if (key == null)
{
throw new InvalidOperationException("The Entity you desire to update does not contain an Id value.");
}
var dbModel = Context.Set<TModel>().Find(key);
var dbEntry = Context.Entry(dbModel);
dbEntry.CurrentValues.SetValues(model);
entry = dbEntry;
//entry.State = EntityState.Modified;
}
var modifiedProps = new Dictionary<string, object>();
foreach (var propertyName in entry.CurrentValues.PropertyNames)
{
// copy only changed values to dict
var prop = entry.Property(propertyName);
if (prop.IsModified)
{
modifiedProps.Add(propertyName, prop.OriginalValue);
}
}
return modifiedProps;
}
Sadly I found no elegant way to get the Key property. But "Id" worked for me. Only the changed properties should appear in the dictionary. Not exactly what you want but something to work with.
Edit: I use the Unit of Work pattern for my DAL. Every repository derives from my base repository, where this code comes from. The update method triggers the GetModifiedProperties() method.
You can than write an update method like that:
UnitOfWork.CutomerRepository.Update(Customer updated, out Dictionary<string, object> changedProps);