I'm using Nhibernate to fetch a collection which has lazy loaded properties but am having trouble returning it as the Serializer tries to serialize the lazy property after the Nhibernate Session is closed. So is there a way to tell NHibernate to give me a true list in which if there were unloaded lazy collections that it would just leave them empty?
For example
IEnumerable<Store> stores = StoreService.GetList(1, 2);
Store has a one-to-many mapping with StockItems which is set to lazy load which then causes the serialization error. I tried
List<Store> stores_r = stores.ToList();
but I get the same thing. Is there something that will traverses through the list and fetches one-to-one relations and ignores one-to-many lazy loading and return a finished list?
Thanks
EDIT:Solution I've tried but still not working
public class NHibernateContractResolver: DefaultContractResolver
{
protected override JsonContract CreateContract(Type objectType)
{
if (typeof(NHibernate.Proxy.INHibernateProxy).IsAssignableFrom(objectType) || typeof(NHibernate.Proxy.ILazyInitializer).IsAssignableFrom(objectType))
{
var oType = objectType.GetInterfaces().FirstOrDefault(i => i.FullName.StartsWith("Navace.Models"));
return oType != null ? base.CreateContract(oType) : base.CreateContract(objectType.BaseType);
}
return base.CreateContract(objectType);
}
protected override List<MemberInfo> GetSerializableMembers(Type objectType)
{
if (typeof(NHibernate.Proxy.INHibernateProxy).IsAssignableFrom(objectType))
{
return base.GetSerializableMembers(objectType.BaseType);
}
else
{
return base.GetSerializableMembers(objectType);
}
}
}
Try to manually serialize so I can use what's happening
IEnumerable<Store> stores = StoreService.GetList(1, 2);
Store> storess = stores.ToList();
JsonSerializer sr = new JsonSerializer
{
ReferenceLoopHandling = ReferenceLoopHandling.Ignore,
ContractResolver = new NHibernateContractResolver(),
NullValueHandling = NullValueHandling.Ignore,
};
StringWriter stringWriter = new StringWriter();
JsonWriter jsonWriter = new Newtonsoft.Json.JsonTextWriter(stringWriter);
sr.Serialize(jsonWriter, storess);
string res = stringWriter.ToString();
The error I get is
Outer exception : Error getting value from 'datedcost' on 'PartProxy'.
Inner exception: No row with the given identifier exists[Navace.Models.Part#0]
My recommendation is to return view models instead of domain models. It's confusing to return an empty collection property when it may have data. By converting the domain model to a view model (using LINQ Select or AutoMapper), the serializer will only touch (and attempt to lazy load) the properties in the view model.
Related
There are many tables in the database that are used as "lookup" tables. All the tables have the same structure, other than the ID column name.
I have found that I can use reflection to open a table and enumerate through the records. The method takes a string (tableName).
Uri serviceUri = new Uri("http://localhost/MyDataService/WcfDataService.svc");
var context = new MyEntities(serviceUri);
var eTable = typeof(MyEntities).GetProperty(tableName).GetValue(context, null) as IEnumerable<object>
foreach (object o in eTable)
...
This works fine, but I want to add a WHERE clause to the query. For example, where InactiveDate == null.
Can I do this? I have been unable to figure this one out.
How about this?
var eTable = (typeof(MyEntities).GetProperty(tableName).GetValue(context, null) as IEnumerable<object>).Where(obj => obj.GetType().GetProperty("InactiveDate").GetValue(obj) == null);
foreach (object o in eTable)
I would suggest to use generics and maybe an interface over reflection.
public function Xyz<TEntity>(Func<MyEntities, IDbSet<TEntity>> dbSetGetter, Expression<Func<TEntity, Boolean>> filter)
{
var serviceUri = new Uri("http://localhost/MyDataService/WcfDataService.svc");
using (var context = new MyEntities(serviceUri))
{
foreach (var entity in dbSetGetter(context).Where(filter))
{
DoSomethingWith(entity);
}
}
}
Usage would be like this
Xyz(context => context.Foo, foo => foo.Bar == 42);
assuming you have an entity Foo with an integer property Bar. The obvious difference to your code is that you have to know the entity type a compile time and I am not sure if you know it then.
I use EF code-first 4.1. in my application. Now I want to get entities through WCF services using generic types.
I'm trying to reflect generic type and invoke the method ToList of DbSet Object.
Here is my code:
public string GetAllEntries(string objectType)
{
try
{
var mdc =
Globals.DbConnection.Create(#"some_db_connection", true);
// Getting assembly for types
var asob = Assembly.GetAssembly(typeof(CrmObject));
// getting requested object type from assembly
var genericType = asob.GetType(objectType, true, true);
if (genericType.BaseType == typeof(CrmObject))
{
// Getting Set<T> method
var method = mdc.GetType().GetMember("Set").Cast<MethodInfo>().Where(x => x.IsGenericMethodDefinition).FirstOrDefault();
// Making Set<SomeRealCrmObject>() method
var genericMethod = method.MakeGenericMethod(genericType);
// invoking Setmethod into invokeSet
var invokeSet = genericMethod.Invoke(mdc, null);
// invoking ToList method from Set<> invokeSet
var invokeToList = invokeSet.GetType().GetMember("ToList").Cast<MethodInfo>().FirstOrDefault();
//this return not referenced object as result
return invokeToList.ToString();
}
return null;
}
catch (Exception ex)
{
return ex.Message + Environment.NewLine + ex.StackTrace;
}
}
In fact then I write the code like return mdc.Set<SomeRealCrmObject>().ToList() - works fine for me! But then I use the generic types I cannot find the method ToList in object DbSet<SomeRealCrmObject>().
Eranga is correct, but this is an easier usage:
dynamic invokeSet = genericMethod.Invoke(mdc, null);
var list = Enumerable.ToList(invokeSet);
C# 4's dynamic takes care of the cumbersome generic reflection for you.
ToLIst() is not a member of DbSet/ObjectSet but is an extension method.
You can try this instead
var method = typeof(Enumerable).GetMethod("ToList");
var generic = method.MakeGenericMethod(genericType);
generic.Invoke(invokeSet, null);
I had a similar situation where I needed a way to dynamically load values for dropdown lists used for search criteria on a page allowing users to run adhoc queries against a given table. I wanted to do this dynamically so there would be no code change on the front or backend when new fields were added. So using a dynamic type and some basic reflection, it solved my problem.
What I needed to do was invoke a DbSet property on a DbContext based on the generic type for the DbSet. So for instance the type might be called County and the DbSet property is called Counties. The load method below would load objects of type T (the County) and return an array of T objects (list of County objects) by invoking the DbSet property called Counties. EntityList is just a decorator object that takes a list of lookup items and adds additional properties needed for the grid on the front-end.
public T[] Load<T>() where T : class
{
var dbProperty = typeof(Data.BmpDB).GetProperties().FirstOrDefault(
x => x.GetMethod.ReturnType.GenericTypeArguments[0].FullName == typeof(T).FullName);
if (dbProperty == null)
return null;
dynamic data = dbProperty.GetMethod.Invoke(BmpDb, null);
var list = Enumerable.ToList(data) as List<T>;
var entityList = new Data.EntityList<T>(list);
return entityList.Results;
}
Is it possible to apply a WHERE clause on a SubSonic query?
For example, I get get a single based on id...
db.Single<Storage>(id);
But how can I get a single based on a simple WHERE clause?
db.Single<Storage>(WHERE columnname == "value");
that's possible:
// Will return a Storage instance with property IsNew = true, if record does not exist
// since an object created with new never can be null
var storage1 = new Storage(1); // id = 1
var storage1 = new Storage(Storag.Columns.ColumnName, "value");
// Will return 0 if record not found (subsonic3 only)
var storage3 = (from s in Storage
where s.ColumnName == "value"
select s).SingleOrDefault();
// Will throw an exception if record not found (subsonic3 only)
var storage3 = (from s in Storage
where s.ColumnName == "value"
select s).Single();
Since db is a partial class you can extend it. Just create a new File within the same namespace (but another folder in your solution). This applies to subsonic 2 but will be similar to subsonic 3, I think.
public static partial class DB
{
public static T Single<T>(String columName, Object columnValue) where T: RecordBase<T>, new()
{
return Select().From<T>()
.Where(columnName).IsEqualTo(columnValue)
.ExecuteSingle<T>();
}
}
Thanks for the above, this was a help and eventually I simplified this to the below...
db.Single<Storage>(s => s.ColumnName == "value");
I am using Entity Framework 4.0 and trying to use the "Contains" function of one the object sets in my context object. to do so i coded a Comparer class:
public class RatingInfoComparer : IEqualityComparer<RatingInfo>
{
public bool Equals(RatingInfo x, RatingInfo y)
{
var a = new {x.PlugInID,x.RatingInfoUserIP};
var b = new {y.PlugInID,y.RatingInfoUserIP};
if(a.PlugInID == b.PlugInID && a.RatingInfoUserIP.Equals(b.RatingInfoUserIP))
return true;
else
return false;
}
public int GetHashCode(RatingInfo obj)
{
var a = new { obj.PlugInID, obj.RatingInfoUserIP };
if (Object.ReferenceEquals(obj, null))
return 0;
return a.GetHashCode();
}
}
when i try to use the comparer with this code:
public void SaveRatingInfo2(int plugInId, string userInfo)
{
RatingInfo ri = new RatingInfo()
{
PlugInID = plugInId,
RatingInfoUser = userInfo,
RatingInfoUserIP = "192.168.1.100"
};
//This is where i get the execption
if (!context.RatingInfoes.Contains<RatingInfo>(ri, new RatingInfoComparer()))
{
//my Entity Framework context object
context.RatingInfoes.AddObject(ri);
context.SaveChanges();
}
}
i get an execption:
"LINQ to Entities does not recognize the method 'Boolean Contains[RatingInfo](System.Linq.IQueryable1[OlafCMSLibrary.Models.RatingInfo], OlafCMSLibrary.Models.RatingInfo,
System.Collections.Generic.IEqualityComparer1[OlafCMSLibrary.Models.RatingInfo])' method, and his method cannot be translated into a store expression."
Since i am not proficient with linQ and Entity Framework i might be making a mistake with my use of the "var" either in the "GetHashCode" function or in general.
If my mistake is clear to you do tell me :) it does not stop my project! but it is essential for me to understand why a simple comparer doesnt work.
Thanks
Aaron
LINQ to Entities works by converting an expression tree into queries against an object model through the IQueryable interface. This means than you can only put things into the expression tree which LINQ to Entities understands.
It doesn't understand the Contains method you are using, so it throws the exception you see. Here is a list of methods which it understands.
Under the Set Methods section header, it lists Contains using an item as supported, but it lists Contains with an IEqualityComparer as not supported. This is presumably because it would have to be able to work out how to convert your IEqualityComparer into a query against the object model, which would be difficult. You might be able to do what you want using multiple Where clauses, see which ones are supported further up the document.
If I have something like:
var query = from children in _data.Children
where children.ChildId == childId
select new CustomModel.MyChild
{
ChildId = children.ChildId,
Name = children.ChildName
};
return query.FirstOrDefault();
Where I want the resultant object to be my custom model.
Can I handle the custom model instantiation in a different method, which could be reused if I had multiple linq queries that all generated a custom child model?
For example,
var query = from children in _data.Children
where children.ChildId == childId
select CreateMyCustomChild([param ??]);
return query.FirstOrDefault();
This may well be impossible, I don't know, but what would the method signature be like if it is possible?
I'm only thinking reuse for when multiple linq queries contain duplicate object initialisation code.
Thanks
It really depends on what version of LINQ you're using. If you're using LINQ to SQL, I don't believe you can call arbitrary methods in the query. The query translator wouldn't know what to do with the method call
If you're using LINQ to Objects, you're absolutely fine to do it, like this:
var query = from children in _data.Children
where children.ChildId == childId
select CreateMyCustomChild(children)
return query.FirstOrDefault();
// Elsewhere
public CustomModel.MyChild CreateMyCustomChild(OtherChild child)
{
return new CustomModel.MyChild
{
ChildId = child.ChildId,
Name = child.ChildName
};
}
(Side note: I'd call the range variable in the query "child" rather than "children" as at any one time it only represents a single child.)
If you wanted you could write "select 1" or in your case "CreateMyCustomChild(children)" since "children" is containing all your info. In your case you aren't adding a lot of info to "children", so why not "select children"?
In other words, just try it out. The return type of your value will determine over which type your LINQ enumerates.
Suppose you had a method that did the transform for you.
public static class Conversions
{
public static CustomModel.MyChild ToCustomModel(this DataModel.MyChild source)
{
return new CustomModel.MyChild()
{
ChildId = source.ChildId,
Name = source.ChildName
}
}
}
You can use such a method to do the conversion of a single item.
DataModel.MyChild myResult = getResult();
CustomModel.MyChild myConvertedResult = myResult.ToCustomModel()
Such a method can also be used in a Enumerable.Select method call.
IEnumerable<DataModel.MyChild> myQueriedResults = getResult();
IEnumerable<CustomModel.MyChild> myConvertedResults =
myQueryiedResults.Select(c => c.ToCustomModel());
While you can do with expressions, I don't think it is worth the hassle. Instead I suggest you define an extension method like:
IQueryable<CustomModel.MyChild> ToModel(this IQueryable<Child> childs)
{
return childs.Select( c=>
select new CustomModel.MyChild
{
ChildId = children.ChildId,
Name = children.ChildName
}
);
}
You can then call:
return _data.Children
.Where(c=>c.ChildId == childId)
.ToModel()
.FirstOrDefault();