I'm using realm swift v1.0.0 and I create an object and I want to update its value permanently.
Following the official guide and some other answers on stackoverflow I've done:
let myobject = MyObjectClass()
myobject.property1 = "test"
try! myrealm.write {
myrealm.add(myobject)
}
And myrealm is a global variable:
let myrealm = try! Realm()
When I recover all the values of MyObjectClass I get back myobject with some initial values set in the init of the class (so the values that I set as initial values are stored properly), but property1 is (null) (as it is declared as an optional string).
But if I look at myobject in the function where I write the code above, its property1 is set to "test", but it's not saved permanently in the Realm db.
Can anyone help me to find out why it doesn't update the value of property1?
I've also tried to do:
try! myrealm.write {
myrealm.add(myobject, update: true)
}
EDIT:
This is my model:
public class MyObjectClass(): Object {
//[...]
public dynamic var property1: String? = nil
public dynamic var property2: MyObjectClass2?
}
Same problem happens with property2 which is another Realm Object.
Related
Could someone give a simple use case example why someone would use copyToRealm() instead of createObject() ?
It is not clear to me why and when would anyone use copyToRealm() if there is createObject().
In the example here they seem pretty much the same https://realm.io/docs/java/latest/ .
copyToRealm() takes an unmanaged object and connects it to a Realm, while createObject() creates an object directly in a Realm.
For example it is very useful when you copy objects generated by GSON - returned from your Rest API into Realm.
realm.createObject() also returns a RealmProxy instance and is manipulated directly and therefore creates N objects to store N objects, however you can use the following pattern to use only 1 instance of object to store N objects:
RealmUtils.executeInTransaction(realm -> {
Cat defaultCat = new Cat(); // unmanaged realm object
for(CatBO catBO : catsBO.getCats()) {
defaultCat.setId(catBO.getId());
defaultCat.setSourceUrl(catBO.getSourceUrl());
defaultCat.setUrl(catBO.getUrl());
realm.insertOrUpdate(defaultCat);
}
});
But to actually answer your question, copyToRealmOrUpdate() makes sense if you want to persist elements, put them in a RealmList<T> and set that RealmList of newly managed objects in another RealmObject. It happens mostly if your RealmObject classes and the downloaded parsed objects match.
#JsonObject
public class Cat extends RealmObject {
#PrimaryKey
#JsonField(name="id")
String id;
#JsonField(name="source_url")
String sourceUrl;
#JsonField(name="url")
String url;
// getters, setters;
}
final List<Cat> cats = //get from LoganSquare;
realm.executeTransaction(new Realm.Transaction() {
#Override
public void execute(Realm realm) {
Person person = realm.where(Person.class).equalTo("id", id).findFirst();
RealmList<Cat> realmCats = new RealmList<>();
for(Cat cat : realm.copyToRealmOrUpdate(cats)) {
realmCats.add(cat);
}
person.setCats(realmCats);
}
});
I'm trying to update an entity using Entity Framework version 6.
I'm selecting the entity from the database like so...
public T Find<T>(object id) where T : class
{
return this._dbContext.Set<T>().Find(id);
}
And updating the entity like so..
public T Update<T>(T entity) where T : class
{
// get the primary key of the entity
object id = this.GetPrimaryKeyValue(entity);
// get the original entry
T original = this._dbContext.Set<T>().Find(id);
if (original != null)
{
// do some automatic stuff here (taken out for example)
// overwrite original property values with new values
this._dbContext.Entry(original).CurrentValues.SetValues(entity);
this._dbContext.Entry(original).State = EntityState.Modified;
// commit changes to database
this.Save();
// return entity with new property values
return entity;
}
return default(T);
}
The GetPrimaryKeyValue function is as so...
private object GetPrimaryKeyValue<T>(T entity) where T : class
{
var objectStateEntry = ((IObjectContextAdapter)this._dbContext).ObjectContext
.ObjectStateManager
.GetObjectStateEntry(entity);
return objectStateEntry.EntityKey.EntityKeyValues[0].Value;
}
Just for clarity. I'm selecting the original entry out as I need to perform some concurrency logic (that Ive taken out). I'm not posting that data with the entity and need to select it manually out of the DB again to perform the checks.
I know the GetPrimaryKeyValue function is not ideal if there's more than one primary key on the entity. I just want it to work for now.
When updating, entity framework coughs up the error below when trying to execute the GetPrimaryKeyValue function.
The ObjectStateManager does not contain an ObjectStateEntry with a reference to an object of type 'NAME_OF_ENTITY_IT_CANNOT_FIND'
I've written many repositories before and I've never had this issue, I cannot seem to find why its not working (hence the post).
Any help would be much appreciated.
Thanks guys!
Steve
It seems like you are having issues getting the PK from the entity being passed in. Instead of trying to go through EF to get this data you could either use their Key attribute or create your own and just use reflection to collect what the key names are. This will also allow you to retrieve multiple keys if it is needed. Below is an example I created inside of LinqPad, you should be able to set it to "Program" mode and paste this in and see it work. Hack the code up and use what you may. I implemented an IEntity but it is not required, and you can change the attribute to anything really.
Here are the results:
Keys found:
CustomIdentifier
LookASecondKey
Here is the code:
// this is just a usage demo
void Main()
{
// create your object from wherever
var car = new Car(){ CustomIdentifier= 1, LookASecondKey="SecretKey", Doors=4, Make="Nissan", Model="Altima" };
// pass the object in
var keys = GetPrimaryKeys<Car>(car);
// you have the list of keys now so work with them however
Console.WriteLine("Keys found: ");
foreach(var k in keys)
Console.WriteLine(k);
}
// you probably want to use this method, add whatever custom logic or checking you want, maybe put
private IEnumerable<string> GetPrimaryKeys<T>(T entity) where T : class, IEntity
{
// place to store keys
var keys = new List<string>();
// loop through each propery on the entity
foreach(var prop in typeof(T).GetProperties())
{
// check for the custom attribute you created, replace "EntityKey" with your own
if(prop.CustomAttributes.Any(p => p.AttributeType.Equals(typeof(EntityKey))))
keys.Add(prop.Name);
}
// check for key and throw if not found (up to you)
if(!keys.Any())
throw new Exception("No EntityKey attribute was found, please make sure the entity includes this attribute on at least on property.");
// return all the keys
return keys;
}
// example of the custom attribute you could use
[AttributeUsage(AttributeTargets.Property)]
public class EntityKey : Attribute
{
}
// this interface is not NEEDED but I like to restrict dal to interface
public interface IEntity { }
// example of your model
public class Car : IEntity
{
[EntityKey] // add the attribure to property
public int CustomIdentifier {get;set;}
[EntityKey] // i am demonstrating multiple keys but you can have just one
public string LookASecondKey {get;set;}
public int Doors {get;set;}
public string Make {get;set;}
public string Model {get;set;}
}
I am getting an error in this line of code Session.Linq<Employees>() :
" An object reference is required for non-static field,method, or property 'System.Web.UI.Page.Session.get'.
This is my code :
public static object GetData(Dictionary<string, object> tableParams)
{
IQueryable<Employees> Employee = Session.Linq<Employees>();
if (tableParams.ContainsKey("sEcho"))
{
var parser = new DataTableParser<Employees>(tableParams, Employee);
return parser.Parse();
}
return Employee;
}
If I use HttpContext.Current.Session.Linq<Employees>();
then i get:
'System.Web.SessionState.HttpSessionState' does not contain a definition for 'Linq' and no extension method 'Linq' accepting a first argument of type 'System.Web.SessionState.HttpSessionState' could be found '
What do i need to do to get this to work? Am I missing a namespace for Linq with regard to Session?I am using System.Linq and System.Linq.Expression.
I think you're misunderstanding something. What you're trying to do doesn't have anything to do with Linq, at least not in the context of retrieving the object from session.
You need to retrieve the object from session and unbox it:
var list = Session["MyList"] as List<int>;
if (list != null)
{
//the list was found and you can start using it here
}
I have an object I want to update in the database. I'm new to EF but have done a fair bit of reading. Clearly my approach is wrong, but I don't understand why. FYI the Context referenced throughout is an ObjectContext which is newly instantiated as this code begins and is disposed immediately after. Here is my Update method - the View is the object I want to update in the database and it has 4 ICollection properties whose changes I also wish to save to the database:
public void Update(View view)
{
var original = Read(view.Username, view.ViewId);
original.ViewName = view.ViewName;
ProcessChanges<CostCentre, short>(Context.CostCentres, original.CostCentres, view.CostCentres, "iFinanceEntities.CostCentres", "CostCentreId");
ProcessChanges<LedgerGroup, byte>(Context.LedgerGroups, original.LedgerGroups, view.LedgerGroups, "iFinanceEntities.LedgerGroups", "LedgerGroupId");
ProcessChanges<Division, byte>(Context.Divisions, original.Divisions, view.Divisions, "iFinanceEntities.Divisions", "DivisionId");
ProcessChanges<AnalysisCode, short>(Context.AnalysisCodes, original.AnalysisCodes, view.AnalysisCodes, "iFinanceEntities.AnalysisCodes", "AnalysisCodeId");
int test = Context.SaveChanges();
}
First I get the original from the database because I want to compare its collections with the new set of collections. This should ensure the correct sub-objects are added and removed. I compare each collection in turn using this ProcessChanges method:
private void ProcessChanges<TEntity, TKey>(ObjectSet<TEntity> contextObjects, ICollection<TEntity> originalCollection, ICollection<TEntity> changedCollection, string entitySetName, string pkColumnName)
where TEntity : class, ILookupEntity<TKey>
{
List<TKey> toAdd = changedCollection
.Select(c => c.LookupKey)
.Except(originalCollection.Select(o => o.LookupKey))
.ToList();
List<TKey> toRemove = originalCollection
.Select(o => o.LookupKey)
.Except(changedCollection.Select(c => c.LookupKey))
.ToList();
toAdd.ForEach(a =>
{
var o = changedCollection.Single(c => c.LookupKey.Equals(a));
AttachToOrGet<TEntity, TKey>(entitySetName, pkColumnName, ref o);
originalCollection.Add(o);
});
toRemove.ForEach(r =>
{
var o = originalCollection.Single(c => c.LookupKey.Equals(r));
originalCollection.Remove(o);
});
}
This compares the new collection to the old one and works out which objects to add and which to remove. Note that the collections all contain objects which implement ILookupEntity.
My problems occur on the line where I call AttachToOrGet. This method I got from elsewhere on stackoverflow. I'm using this because I was often getting a message saying that "An object with the same key already exists in the ObjectStateManager" when attaching a new subobject. Hopefully you'll understand my confusion around this when I post the code of this method below:
public void AttachToOrGet<TEntity, TKey>(string entitySetName, string pkColumnName, ref TEntity entity)
where TEntity : class, ILookupEntity<TKey>
{
ObjectStateEntry entry;
// Track whether we need to perform an attach
bool attach = false;
if (Context.ObjectStateManager.TryGetObjectStateEntry(new EntityKey(entitySetName, pkColumnName, entity.LookupKey), out entry))
//if (Context.ObjectStateManager.TryGetObjectStateEntry(Context.CreateEntityKey(entitySetName, entity), out entry))
{
// Re-attach if necessary
attach = entry.State == EntityState.Detached;
// Get the discovered entity to the ref
entity = (TEntity)entry.Entity;
}
else
{
// Attach for the first time
attach = true;
}
if (attach)
Context.AttachTo(entitySetName, entity);
}
Basically this is saying if the entity is not already attached then attach it. But my code is returning false on the Context.ObjectStateManager.TryGetObjectStateEntry line, but throwing an exception on the final line with the message "An object with the same key already exists in the ObjectStateManager". To me this is paradoxical.
As far as I'm concerned I'm trying to achieve something very simple. Something it would take 20 minutes to write a stored procedure for. A simple database update. Frankly I don't care what is attached and what isn't because I don't wish to track changes or create proxies or lazy load or do anything else EF offers me. I just want to take a very simple object and update the database using a minimal number of trips between servers. How is this so complicated? Please someone help me - I've spent a whole day on this!
Update
Here's my ILookupEntity class:
public interface ILookupEntity<TKey>
{
TKey LookupKey { get; }
string DisplayText { get; }
}
Here's how it is implemented in CostCentre:
public partial class CostCentre : IFinancialCode, ILookupEntity<short>
{
#region IFinancialCode Members
public short ID { get { return CostCentreId; } }
public string DisplayText { get { return string.Format("{0} - {1}", Code, Description); } }
#endregion
#region ILookupEntity Members
public short LookupKey
{
get { return ID; }
}
#endregion ILookupEntity Members
}
Well, I've worked through this and found a solution, but I can't say I understand it. The crucial ingredient came when I was performing a check after the comment by #Slauma. I wanted to check I was using the correct entity set name etc so I included the following lines near the top of my AttachToOrGet method:
var key = new EntityKey(entitySetName, pkColumnName, entity.LookupKey);
object temp;
if (!Context.TryGetObjectByKey(key, out temp))
throw new Exception(string.Format("No entity was found in {0} with key {1}", entitySetName, entity.LookupKey));
Bizarrely this alone resolved the problem. For some reason, once I'd called the TryGetObjectByKey then the ObjectStateManager.TryGetObjectStateEntry call actually started locating the attached entity. Miraculous. I'd love it if anyone can explain this.
By the way, I also needed to include the following code, but that's just because in my case the modelled entities are located in a separate assembly from the context itself.
Assembly assembly = typeof(CostCentre).Assembly;
Context.MetadataWorkspace.LoadFromAssembly(assembly);
I'm learning scala and can't find out how to do this:
I'm doing a mapper between scala objects and google appengine entities, so if i have a class like this:
class Student {
var id:Long
var name:String
}
I need to create an instance of that class, in java i would get the Field by it's name and then do field.set(object, value) but I can't find how to do so in scala.
I can't use java reflection since the fields of Student are seen as private and field.set throws an error because of that.
Thanks
Scala turns "var" into a private field, one getter and one setter. So in order to get/set a var by identifying it using a String, you need to use Java reflection to find the getter/setter methods. Below is a code snippet that does that. Please note this code runs under Scala 2.8.0 and handlings of duplicated method names and errors are nonexistent.
class Student {
var id: Long = _
var name: String = _
}
implicit def reflector(ref: AnyRef) = new {
def getV(name: String): Any = ref.getClass.getMethods.find(_.getName == name).get.invoke(ref)
def setV(name: String, value: Any): Unit = ref.getClass.getMethods.find(_.getName == name + "_$eq").get.invoke(ref, value.asInstanceOf[AnyRef])
}
val s = new Student
s.setV("name", "Walter")
println(s.getV("name")) // prints "Walter"
s.setV("id", 1234)
println(s.getV("id")) // prints "1234"