i am trying to set the redux state but not the whole object tree but just a sub-tree.
Object graph -
Parent
|----Header
|----Summary
|-----List of objects
I am using following code -
return state.setIn([Parent, 'Summary'], summary)
It sets the summary object but the list of objects is null. What am I doing wrong ?
you can try it in this way:
let newSummary = Object.assign(Parent.summary, {...yourchange});
this.setState(Object.assign(Parent.summary, {
summary: newSummary
})})
Related
In Vue, provide can pass values to child components
provide('data',ref("I am data for child components"))
Subcomponents can use inject to get the value.
How to get the data in the parent component? ?
Normal pass by value:
let data = ref("I am data for child components");
provide('data',data);//This way the parent component can get
it and the child component can get it too
Transfer Function:
let children = ref('')
function data(val){
children.value = val;//Get the value passed by the child component
}
provide('data',data);
Sub: let getData = inject('data',data)
data is a function, you can getData('data for father')
Built-in queries to Spring Data Neo4j (SDN) return objects populated with depth 1 by default. This means that "children" (related nodes) of an object returned by a query are populated. That's good - there are actual objects on the end of references from objects returned by these queries.
Custom queries are depth 0 by default. This is a hassle.
In this answer, it is described how to get springboot neo4j to populate a related element to the target of a custom query - to achieve an extra one level of depth of results from the query.
I am having trouble with this method when the related elements are in a list:
#NodeEntity
public class BoardPosition {
#Relationship(type="PARENT", direction = Relationship.INCOMING)
public List<BoardPosition> children;
I have a query returning a target BoardPosition and I need it's children to be populated.
#Query("MATCH (target:BoardPosition) <-[c:PARENT]- (child:BoardPosition)
WHERE target.play={Play}
RETURN target, c, child")
BoardPosition findActiveByPlay(#Param("Play") String play);
The problem is that the query appears to return one separate result for each child, and those results aren't being used to populate the array of children in the target.
Instead of Spring Neo collating the children into the array on the target, I get "only 1 result expected" error - as if the query is returning multiple results each with one child, rather than one result with the children in it.
org.springframework.dao.IncorrectResultSizeDataAccessException:
Incorrect result size: expected at most 1
How can I have a custom query to populate that target's children list?
(Note that the built-in findByPlay(play) does what I want - the built-in queries have a depth of 1 rather than 0, and it returns a target with populated children - but of course I need to make the query a bit more sophisticated than just "by Play"... that's why I need to solve this)
Versions:
org.springframework.data:spring-data-neo4j:5.1.3.RELEASE
neo4j 3.5.0
=== Edit ======
Your problem arises because you have self-relationship (relationship between nodes of the same label)
This is how Spring treat your query for single node:
org.springframework.data.neo4j.repository.query.GraphQueryExecution
#Override
public Object execute(Query query, Class<?> type) {
Iterable<?> result;
....
Object ret = iterator.next();
if (iterator.hasNext()) {
throw new IncorrectResultSizeDataAccessException("Incorrect result size: expected at most 1", 1);
}
return ret;
}
Spring passes your node class type Class<?> type to neo4j-ogm and have your data read back.
You know, neo4j server will returns multiple rows for your query, one for each matching path:
A <- PARENT - B
A <- PARENT - C
A <- PARENT - D
If your nodes are of different labels, i.e. of different class type then the ogm only return single node correspond to your query return type, no problem.
But your nodes are of the same labels, i.e. same class type => Neo4j OGM cannot distinguish which is the returned node -> All nodes A, B, C, D returned -> Exception
Regard this issue, I think you should file a bug report now.
For workaround, you can can change the query to return only the distinct target.your_identity_property (identity_property is 'primary key' of the node, which uniquely identify your node)
Then have your application call load with the that identity property:
public interface BoardRepository extends CrudRepository<BoardPos, Long> {
#Query("MATCH (target:B) <-[c:PARENT]- (child:B) WHERE target.play={Play} RETURN DISTINCT target.your_identity_property")
Long findActiveByPlay(#Param("Play") String play);
BoardPos findByYourIdentityProperty(xxxx);
}
=== OLD ======
Spring docs says that (highlighted by me):
Custom queries do not support a custom depth. Additionally, #Query does not support mapping a path to domain entities, as such, a path should not be returned from a Cypher query. Instead, return nodes and relationships to have them mapped to domain entities.
So clearly your use-case (populate children nodes by custom query) is supported. Spring framework already maps the results into a single node. (Indeed, my setup on local turnouts that the operation is working properly)
So your exception may be caused by several issues:
You have more than one target:BoardPosition with target.play={play}. So the exception refers to more than one target:BoardPosition instead of one BoardPosition with multiple child result
You have incorrect entity mapping. Do you have your mapping field annotated with #Relationship with correct direction attribute? You might post your entity here.
Here is my local setup:
#NodeEntity(label = "C")
#Data
public class Child {
#Id
#GeneratedValue
private long id;
private String name;
#Relationship(type = "PARENT", direction = "INCOMING")
private List<Parent> parents;
}
public interface ChildRepository extends CrudRepository<Child, Long> {
#Query("MATCH (target:C) <-[p:PARENT]- (child:P) "
+ "WHERE target.name={name} "
+ "RETURN target, p, child")
Child findByName(#Param("name") String name);
}
(:C) <-[:PARENT] - (:P)
Consider the alternative query
MATCH (target:BoardPosition {play:{Play}})
RETURN target, [ (target)<-[c:PARENT]-(child:BoardPosition) | [c, child] ]
which is using list comprehension to return not only the target but also its relations and related nodes of label BoardPosition within one result row. This ensures that the result will be a single row (as long as your attribute play is unique).
I didn't try it with your example but in my application this approach is working fine. Neo4j OGM hydrates the objects as expected. It is important to include the related nodes as well as the relations pointing to the nodes.
If you enable neo4j OGM logs, you can see that the build-in queries with depth 1 use the same approach.
I have a Collection and a Member Managed Object in Core Data.
Collection has a to-many relationship members, that can contain Member objects. Member objects should be uniquely associated to a single Collection.
I want to be able to use the objects in this relationship as Managed Objects for use in populating my Table View Controller, like so:
let members : [Member] = someCollection.members
However, the members property seems to be an NSOrderedSet? object, and not an array of Member.
To this extent, I have tried the following (found on the internet, as I'm very new to Swift) and I am also trying to catch the situation where the relationship field could be nil. It doesn't work for me, and I don't understand why.
let members = someCollection.members?.array as! [Member]
if members != nil {
//Do something with the array
else {
//handle the case that there is no entry in the relationship field
}
I am getting the following error:
Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value
Please help me understand what I am doing wrong, and if possible, provide a solution.
Since array returns a non-optional you have to optional bind members. If the check succeeds you can safely force unwrap the array. The code checks also if the array is not empty.
if let members = someCollection.members, members.count > 0 {
let memberArray = members.array as! [Member]
//Do something with the array
else {
//handle the case that there is no entry in the relationship field
}
I have a class called Structure:
public class Structure
{
public int StructureId { get; set; }
public Structure Parent { get; set; }
}
As you can see, Structure has a parent Structure. There can be an indefinite number of structures within this hierarchy.
Is there any way, using LINQ (with Entity Framework), to get the top-most structure in this hierarchy?
Currently, I'm having to hit the database quite a few times in order to find the top most parent. The top most parent is a Structure with a null Parent property:
Structure structure = structureRepository.Get(id);
while (structure.Parent != null)
{
structure = structureRepository.Get(structure.Parent.StructureId);
}
// When we're here; `structure` is now the top most parent.
So, is there any elegant way to do this using LINQ/Lambdas? Ideally, starting with the following code:
var structureQuery = from item in context.Structures
where item.StructureId == structureId
select item;
I just want to be able to write something like the following so that I only fire off one database hit:
structureQuery = Magic(structureQuery);
Structure topMostParent = structureQuery.Single();
This is not a direct answer, but the problem you are having is related to the way you are storing your tree. There are a couple ways of simplifying this query by structuring data differently.
One is to use a Nested Set Hierarchy, which can simplify many kinds of queries across trees.
Another is to store a denomralized table of Ancestor/Descendant/Depth tuples. This query then becomes finding the tuple with the current structure as the descendant with the maximum depth.
I think the best I'm going to get is to load the entire hierarchy in one hit from the structure I want the top parent of:
var structureQuery = from item in context.Structures
.Include(x => x.Parent)
where item.StructureId == structureId
select item;
Then just use the code:
while (structure.Parent != null)
{
structure = structure.Parent;
}
I have a similar situation. I didn't manage to solve it directly with LINQ/EF. Instead I solved by creating a database view using recursive common table expressions, as outlined here. I made a user-defined function that cross applies all parents to a child (or vice versa), then a view that makes use of this user-defined function which I imported into my EF object context.
(disclaimer: simplified code, I didn't actually test this)
I have two tables, say MyTable (containing all items) and MyParentChildTable containing the ChildId,ParentId relation
I have then defined the following udf:
CREATE FUNCTION dbo.fn_getsupertree(#childid AS INT)
RETURNS #TREE TABLE
(
ChildId INT NOT NULL
,ParentId INT NULL
,Level INT NOT NULL
)
AS
BEGIN
WITH Parent_Tree(ChildId, ParentId)
AS
(
-- Anchor Member (AM)
SELECT ChildId, ParentId, 0
FROM MyParentChildTable
WHERE ChildId = #childid
UNION all
-- Recursive Member (RM)
SELECT info.ChildId, info.ParentId, tree.[Level]+1
FROM MyParentChildTable AS info
JOIN Parent_Tree AS tree
ON info.ChildId = tree.ParentId
)
INSERT INTO #TREE
SELECT * FROM Parent_Tree;
RETURN
END
and the following view:
CREATE VIEW VwSuperTree AS (
SELECT tree.*
FROM MyTable
CROSS APPLY fn_getsupertree(MyTable.Id) as tree
)
GO
This gives me for each child, all parents with their 'tree level' (direct parent has level 1, parent of parent has level 2, etc.). From that view, it's easy to query the item with the highest level. I just imported the view in my EF context to be able to query it with LINQ.
I like the question and can't think of a linq-y way of doing this. But could you perhaps implement this on your repository class? After all, there should be only one at the top and if the need for it is there, then maybe it deserves a structureRepository.GetRoot() or something.
you can use the linq take construct, for instance
var first3Customers = (
from c in customers
select new {c.CustomerID, c.CustomerName} )
.Take(2);
I've thrown myself headfirst into C# and .Net 2.0 using Linq, and I'm having a few problems debugging some of the problems, namely the following:
I have a ComboBox control (cmbObjects) I want to populate with a set of objects retrieved using Linq. I've written a helper method to populate a List<T> generic:
class ObjectProvider
{
public static List<T> Get<T>(bool includeNull) where T : class, new()
{
List<T> list = new List<T>();
LutkeDataClassesDataContext db = ConnectionManager.GetConnection();
IQueryable<T> objects = db.GetTable<T>().AsQueryable();
if (includeNull) list.Add(null);
foreach (T o in objects) list.Add(o);
return list;
}
public static List<T> Get<T>() where T : class, new()
{
return Get<T>(false);
}
}
I verified the results when calling the function with true or false - the List does contain the right values, when passing true, it contains null as the first value, followed by the other objects.
When I assign the DataSource to the ComboBox however, the control simply refuses to display any items, including the null value (not selectable):
cmbObjects.DataSource = ObjectProvider.Get<Car>(true);
Passing in false (or no parameter) does work - it displays all of the objects.
Is there a way for me to specify a "null" value for the first object without resorting to magic number objects (like having a bogus entry in the DB just to designate a N/A value)? Something along the lines of a nullable would be ideal, but I'm kind of lost.
Also, I've tried adding new T() instead of null to the list, but that only resulted in an OutOfMemoryException.
The combo box control has an option to append data bound items to the hard-coded items in the list. So you hard-code your n/a value, and data bind the real values.
Okay, it seems the DataSource becomes invalid if you try to add a null value. The solution was to just add the items via a simple foreach loop with an empty string at the start instead of assigning the List<>.