There's a possibility to find a objects using similar expression as below?
List<Object> findPracticesByHeadquartersCityRegionOrInstitutionsCityRegion(List<Region> regions)
The object looks like this:
public class Practice{
private Headquarters headquarters;
private List<Institution> institutions;
}
The Headquarters and an Institution have the variable City.
City have the variable of Region.
Problem is a List. Is possible to did something similar to loop inside query to check every object inside this list?
I use mongodb.
Regards,
Thank you in advance
Related
I've been struggling with a problem with one of my lists of data because one of the requirements after generating it is to group some of them by some common parameters (more than 1)
What I should get at the end is a map where the value is a list of common objects. For example.
List<Cause> listToGroup = new ArrayList<>();
listToGroup.add(Similar);
listToGroup.add(Common);
listToGroup.add(Similar);
listToGroup.add(Similar);
listToGroup.add(Common);
In a weird way to represent one group (Similar) and the other (Common), those should be separated into two different lists (that list is generated by a request to other methods, in that case, I just added manually to show what could be the contained data in the list). My main problem is the criteria to group them because is based on a group of parameters that are shared, but not all (if the required parameters are equal, should belong to the same list) In the class shown below, that behaviour is seen because there are some parameters that are not being considered.
public class Cause extends GeneralDomain {
//parameters which must be equals between objects
private Long id;
private Date creationDate;
private Part origin;
private Part destination;
//parameters which are not required to be equal
private BigDecimal value
private Stage stageEvent
//omitted getters and setters
}
I've been seeing the comparator method and the groupingBy method provided in Java 8, but at the moment I just know how to perform that task considering just one parameter (for example grouping them by id) And I have no idea about how to group them using more than one parameter.
//this should be the code if the requirement would be just one parameter to groupby, but in my case are more than one.
Map<Long, List<Cause>> result = request.getList(criteria)
.stream()
.map(p -> parsin.createDto(p))
.collect(groupingBy(Cause ::getId));
I would be really glad for any suggestion. If my explanation is not clear, I'm so sorry. That became so complicated that even is hard for me to explain
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 have a question regarding list comparator. I have a web application which have page with table.
I can edit data in this table and also delete row.
Standard comparator working correct when i edit data but i have problem when i remove row.
The problem is common (i think) when i remove e.g one row what is happening
javers comparing old list with now one it's looks something like this:
old list have two object now list have one object (i removed first one) now javers don't know which object
was removed and he compare first object from old list with second object from new list and for him
whole object was changed and that is not true.
My thought was I will wrote own list comparator and in this comparator before javers compare method will be colled
i check if comparing objects have the same ID.
Unfortunately i have problem to obtain object ID.
My comparator looks like this
public class ListComperator implements CustomPropertyComparator {
public ValueChange compare(List list1, List list2, GlobalId globalId, Property property) {
for (Object o1 : list1) {
for (Object o2 : list2) {
if(o1.getId().equals(o2.getId()) ) {
javers.compare(o1, o2);
}
}
}}}
The second list "list2" have my object from which i can get any property e.g ID.
The firs list "list1" is list with some ValueObjectId and i don't know how to get property with id from object o1.
Is there a way to get this information or maybe i'm doing something totally wrong please help.
I suppose that you have ValueObjects stored in those Lists? Since ValueObjects has no identifiers, there is no way to detect how they 'move' between List indexes when List is changed. Custom comparator won't help much without a
way to identify you objects.
I suggest to add some kind of identifiers to your objects stored in a List and map them as Entities (use #Id annotation).
For some reason I am totally stuck on the syntax for LINQ Group in vb.net - can somebody help me sort out the following?
I have 5000 objects like this:
Public Class ExpressionReturn
Implements IComparable(Of ExpressionReturn)
Public Property Price As Price
Public Property Value As Nullable(Of Decimal)
Public Property Expression As Expression
Public Property Rank As Single
End Class
I am trying to group them together on price.priceid (an integer) and then return a sum of the ranks to have a series of object such as this:
Public Class RankReturn
Public Property Price As Price
Public Property Expression As Expression
Public Property RankSum As Single
End Class
I'm stuck on the syntax for Group By in Linq... can anyone help?
Thanks for coming back to me - after playing with the code with a clear head it seems a big difference between c# (which has most of the examples) and vb.net is that you seem to have to return the same objects in the select statement as are being grouped.
I've now ditched this approach as grouping is much slower than I expected - I've used a dictionary to store the sum that I need which is much quicker 5ms compared to 700ms!
I'm working on a custom linq extension for nHibernate by extending the BaseHqlGeneratorForMethod. The technique is documented here:
http://fabiomaulo.blogspot.com/2010/07/nhibernate-linq-provider-extension.html
I've had success with implementing these for various types of operations, but I must say - converting a simple linq expression to its full expression tree is not easy! I'm stuck on one now.
For this example, I have three entities. Employee, Group, and EmployeeGroup. The EmployeeGroup class sets up a many-to-many relationship between Employee and Group. I must specifically create the intermediate class because there are additional properties to track like specific permissions each employee has in each group. So there are two one-to-many relationships, rather than an nHibernate many-to-many relationship.
Now say I want to get all groups that contain a specific employee. I can write this query:
var groups = session.Query<Group>()
.Where(g => g.EmployeeGroups.Any(eg => eg.Employee == employee));
This works fine, but it's a lot to type. I'd much rather be able to do this:
var groups = session.Query<Group>().Where(g => g.HasEmployee(employee));
I start by creating an extension method like so:
public static bool HasEmployee(this Group group, Employee employee)
{
return group.EmployeeGroups.Any(eg => eg.Employee == employee);
}
This works when querying a local list of groups, but not against the nHibernate session. For that, I have to also create a linq extension and register it. Just like in the article (linked above), I create a GroupHasEmployeeGenerator class that extends BaseHqlGeneratorForMethod. I set its .SupportedMethods property to reference my HasEmployee extension method.
Where I get lost is in the override to BuildHql. The expression to build gets complicated pretty fast. I figure since I'm replacing the .Any clause - a good place to start is with the source for the built-in AnyHqlGenerator class. But that doesn't take into account that the source is a property of the original element, and it also doesn't take into account that I don't have a lambda expression to represent the where clause. I need to build these parts manually.
There's no point in posting my attempts so far, as they've all be quite far from anything that would work.
Will someone please help me convert this simple expression into the approprate set of methods for the BuildHql method override?
If there is any better documentation out there for this, please let me know. Thanks.
I know this question is a year old, but I ran into a very similar issue when implementing BaseHqlGeneratorForMethod today.
The input to BuildHql contains a collection of System.Linq.Expressions.Expression arguments that are passed to your extension method. Using these arguments, you can build an expression tree that represents the implementation of your extension method. If the resulting expression is something NHibernate.Linq supports, then you can transform that expression to a subtree of Hql using the provided IHqlExpressionVisitor.
In your example:
public static bool HasEmployee(this Group group, Employee employee)
{
return group.EmployeeGroups.Any(eg => eg.Employee == employee);
}
This would become something similar to this:
public override HqlTreeNode BuildHql(MethodInfo method, Expression targetObject, ReadOnlyCollection<Expression> arguments, HqlTreeBuilder treeBuilder, IHqlExpressionVisitor visitor)
{
var AnyMethod = EnumerableHelper.GetMethod("Any", new[] {typeof(IEnumerable<EmployeeGroup>), typeof(Func<EmployeeGroup, bool>)}, new[] {typeof(EmployeeGroup)});
var EmployeeGroupsProperty = ReflectionHelper.GetProperty<Group>(g => g.EmployeeGroups);
var EmployeeProperty = ReflectionHelper.GetProperty<EmployeeGroup>(eg => eg.Employee);
var EmployeeGroupParameter = Expression.Parameter(typeof(EmployeeGroup));
var EmployeeGroupPredicate = Expression.Lambda(Expression.Equal(Expression.MakeMemberAccess(EmployeeGroupParameter, EmployeeProperty), arguments[1]), EmployeeGroupParameter);
var CallExpression = Expression.Call(AnyMethod, Expression.MakeMemberAccess(arguments[0], EmployeeGroupsProperty), EmployeeGroupPredicate);
return visitor.Visit(CallExpression);
}
I can't really test this specific example, but the same approach worked for me when providing support for my own extension method.