In our application, we have various objects set to lazy false based on the application needs. However, in one of the use case we want to ignore all the lazy settings within the HBM files, and get ONLY the target object.
So the question is: is there a way to specify in the HQL to fetch ONLY the target object irrespective of the HBM settings?
~Sri
you can use setFetchMode on the Criteria before it is executed to override the HBM file setting
Sorry, not sure if you understood your question.
If you have to implement it for a specific class, you can just use SetFetchMode.
var query = session.CreateCriteria(typeof(MyClass));
query.SetFetchMode("PropertyA", FetchMode.Select);
query.SetFetchMode("PropertyB", FetchMode.Select);
Note: for many-to-one references the entity class itself must be mapped with lazy=true. If not, NHibernate doesn't even create a proxy class for it.
This is the answer if you want to lazy load the type in a generic, type-independent way:
You could find them with the metadata and add fetch modes to a criteria
I didn't try it, but I would start with the following code:
var meta = sessionfactory.GetClassMetaData(typeof(MyClass));
var query = session.CreateCriteria(typeof(MyClass));
for(int index = 0; index < meta.PropertyType.Length; index++)
{
if (meta.PropertyType[index] == NHibernateUtil.Entity)
{
query.SetFetchMode(meta.PropertyNames[index], FetchMode.Select);
}
}
This doesn't include collections. They are probably found with factory.GetCollectionMetadata(roleName), but you need to find out the roleName.
Related
Is there a way to restrict the "columns" returned from a Realm Xamarin LINQ query?
For example, if I have a Customer RealmObject and I want a list of all customer names, do I have to query All<Customer> and then enumerate the results to build the names list? That seems cumbersome and inefficient. I am not seeing anything in the docs. Am I missing something obvious here? Thanks!
You have to remember that Realm is an object based store. In a RDBMS like Sqlite, restricting the return results to a sub-set of "columns" of an "record" makes sense, but in an object store, you would be removing attributes from the original class and thus creating a new dynamic class to then instantiate these new classes as objects.
Thus is you want just a List of strings representing the customer names you can do this:
List<string> names = theRealm.All<Customer>().ToList().Select(customer => customer.Name).ToList();
Note: That you take the Realm.All<> results to a List first and then using a Linq Select "filter" just the property that you want. Using a .Select directly on a RealmResults is not currently supported (v0.80.0).
If you need to return a complex type that is a subset of attributes from the original RealObject, assuming you have a matching POCO, you can use:
var custNames = theRealm.All<Customer>().ToList().Select((Customer c) => new Name() { firstName = c.firstName, lastName = c.lastName } );
Remember, once you convert a RealmResult to a static list of POCOs you do lose the liveliness of using RealmObjects.
Personally I avoid doing this whenever possible as Realm is so fast that using a RealmResult and thus the RealObjects directly is more efficient on processing time and memory overhead then converting those to POCOs everytime you need to new list...
I using Query DSL generated entity EntitySerializer in order to query JPA entities using QueryDSL (integrated with SpringData).
I’m receiving from the client property names and I want to create predicates for the properties that can be added (AND) to additional predicats.
I don’t know how to get from the EntitySerializer the predicate/Path that matches my property name. For example, let’s say we have a Person entity (with auto generated QPerson class) with a “name” property that I want to filter on (at the end I want to create a generic method). Here is the generic method:
Public Predicat getPredicatByPropertyName(String propertyName) {
QPerson p = QPerson.person;
person.getPredicat(“propertyName”).like(“tom”);
}
To create a String typed property just use the following snippet
new StringPath(p, propertyName)
which can then be used like this to create a Predicate instance
new StringPath(p, propertyName).like("tom")
I did it slightly different since as Timo said didn't work straightforward, here is it:
query.from(play);
query.where( Expressions.stringPath(play, "name").eq("New play") );
I know it could also be achieved by doing it separately:
StringPath column = Expressions.stringPath(play, "name");
query.from(play);
query.where( column.eq("New play") );
As of QueryDSL 5.0, I found two ways to do this independent of the column class:
First way: using just reflection:
Field pathField = p.getClass().getField(reportField.getFieldName());
ComparableExpressionBase<?> path = (ComparableExpressionBase<?>)
pathField.get(p);
Note: I use the ComparableExpressionBase class because it is extendend by all "path classes" that I found and it also can be used in select, orderBy and other functions to build the query
Second way: using reflection and ExpressionUtils:
Class<?> pParameterClass = (Class<?>) ((ParameterizedType) p.getClass().getGenericSuperclass())
.getActualTypeArguments()[0];
Class<?> pathClass = pParameterClass.getDeclaredField(pathName).getDeclaringClass();
Path<?> path = ExpressionUtils.path(pathClass, p, pathName);
Note: using this way we first get the class of the entity of the table see this answer for an explanation on how to get a parametrized type. Next, we get the class of the path and finally we get the path with the ExpressionUtils.path method.
I have an Abstract type called Product, and five "Types" that inherit from Product in a table per type hierarchy fashion as below:
I want to get all of the information for all of the Products, including a smattering of properties from the different objects that inherit from products to project them into a new class for use in an MVC web page. My linq query is below:
//Return the required products
var model = from p in Product.Products
where p.archive == false && ((Prod_ID == 0) || (p.ID == Prod_ID))
select new SearchViewModel
{
ID = p.ID,
lend_name = p.Lender.lend_name,
pDes_rate = p.pDes_rate,
pDes_details = p.pDes_details,
pDes_totTerm = p.pDes_totTerm,
pDes_APR = p.pDes_APR,
pDes_revDesc = p.pDes_revDesc,
pMax_desc = p.pMax_desc,
dDipNeeded = p.dDipNeeded,
dAppNeeded = p.dAppNeeded,
CalcFields = new DAL.SearchCalcFields
{
pDes_type = p.pDes_type,
pDes_rate = p.pDes_rate,
pTFi_fixedRate = p.pTFi_fixedRate
}
}
The problem I have is accessing the p.pTFi_fixedRate, this is not returned with the Products collection of entities as it is in the super type of Fixed. How do I return the "super" type of Products (Fixed) properties using Linq and the Entity Framework. I actually need to return some fields from all the different supertypes (Disc, Track, etc) for use in calculations. Should I return these as separate Linq queries checking the type of "Product" that is returned?
This is a really good question. I've had a look in the Julie Lerman book and scouted around the internet and I can't see an elegant answer.
If it were me I would create a data transfer object will all the properties of the types and then have a separate query for each type and then union them all up. I would insert blanks into the DTO properies where the properties aren't relevant to that type. Then I would hope that the EF engine makes a reasonable stab at creating decent SQL.
Example
var results = (from p in context.Products.OfType<Disc>
select new ProductDTO {basefield1 = p.val1, discField=p.val2, fixedField=""})
.Union(
from p in context.Products.OfType<Fixed>
select new ProductDTO {basefield1 = p.val1, discField="", fixedField=p.val2});
But that can't be the best answer can it. Is there any others?
So Fixed is inherited from Product? If so, you should probably be querying for Fixed instead, and the Product properties will be pulled into it.
If you are just doing calculations and getting some totals or something, you might want to look at using a stored procedure. It will amount to fewer database calls and allow for much faster execution.
Well it depends on your model, but usually you need to do something like:
var model = from p in Product.Products.Include("SomeNavProperty")
.... (rest of query)
Where SomeNavProperty is the entity type that loads pTFi_fixedRate.
I have run sqlmetal.exe agaisnt my database.
SqlMetal.exe /server:server /database:dbname /code:mapping.cs
I have included this into my solution. So I can now create an object for each of the database tables. Great. I now wish to use ling to query by database. Can I presume that none of the connection etc is handled by the output of sqlmetal.exe. If this is correct what ways can I use ling to query my database?
Does the generated code include a Data Context (a class which inherits from System.Data.Linq.DataContext)? If so, then that's probably what you're looking for. Something like this:
var db = new SomeDataContext();
// You can also specify a connection string manually in the above constructor if you want
var records = db.SomeTable.Where(st => st.id == someValue);
// and so on...
how can I build a table of "orders" containing "IdOrder", "Description" and "User"?... the "User" field is a reference to the table "Users", which has "IdUser" and "Name". I'm using repositories.
I have this repository:
Repository<Orders> ordersRepo = new OrderRepo<Orders>(unitOfWork.Session);
to return all Orders to View, I just do:
return View(ordersRepo.All());
But this will result in something like:
IdOrder:1 -- Description: SomeTest -- User: UserProxy123ih12i3123ih12i3uh123
-
When the expected result was:
IdOrder:1 -- Description: SomeTest -- User: Thiago.
PS: I don't know why it returns this "UserProxy123ih12i3123ih12i3uh123". In Db there is a valid value.
The View:
It is showed in a foreach (var item in Model).
#item.Description
#item.User //--> If it is #item.User.Name doesn't work.
What I have to do to put the Name on this list? May I have to do a query using LINQ - NHibernate?
Tks.
What type of ORM are you using? You mention "repositories" but does that mean LinqToSql, Entity Framework, NHibernate, or other?
It looks like you are getting an error because the User field is not loaded as part of the original query. This is likely done to reduce the size of the result set by excluding the related fields from the original query for Orders.
There are a couple of options to work around this:
Set up the repository (or context, depending on the ORM) to include the User property in the result set.
Explicitly load the User property before you access it. Note that this would be an additional round-trip to the database and should not be done in a loop.
In cases where you know that you need the User information it would make sense to ensure that this data in returned from the original query. If you are using LinqToSql take a look at the DataLoadOptions type. You can use this type to specify which relationships you want to retrieve with the query:
var options = new DataLoadOptions();
options.LoadWith<Orders>(o => o.User);
DataContext context = ...;
context.LoadOptions = options;
var query = from o in context.Orders
select o;
There should be similar methods to achive the same thing whatever ORM you are using.
In NHibernate you can do the following:
using (ISession session = SessionFactory.OpenSession())
{
var orders = session.Get<Order>(someId);
NHibernateUtil.Initialize(orders.User);
}
This will result in only two database trips (regardless of the number of orders returned). More information on this can be found here.
In asp.net MVC the foreign key doesn't work the way you are using it. I believe you have to set the user to a variable like this:
User user = #item.User;
Or you have to load the reference sometimes. I don't know why this is but in my experience if I put this line before doing something with a foreign key it works
#item.UserReference.load();
Maybe when you access item.User.Name the session is already closed so NHib cannot load appropriate user from the DB.
You can create some model and initialize it with proper values at the controller. Also you can disable lazy loading for Orders.User in your mapping.
But maybe it is an other problem. What do you have when accessing "#item.User.Name" from your View?