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MySQL fetch parent and all children


MySQL fetch parent and all children

By : Min Tan
Date : November 22 2020, 02:59 PM
To fix the issue you can do My database looks something like: , You can use GROUP_CONCAT:
code :
SELECT ID, Name
FROM (
  SELECT p.ID, p.Name, GROUP_CONCAT(c.Name ORDER BY c.Name) AS children
  FROM Parent AS p
  INNER JOIN Children AS c ON p.ID = c.Parent
  GROUP BY p.ID, p.Name) AS t
WHERE t.children = 'Bob,Jack,Smith'


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How to fetch a collection of children applying filters on both parent and children

How to fetch a collection of children applying filters on both parent and children


By : imAProgrammer
Date : March 29 2020, 07:55 AM
like below fixes the issue this looks like Linq2Objects, therefor the IList Results contains duplicate records, probably you do eager fetching to levels deep which unfortunatly results in duplicate root entities. use distinctrootentity-resulttransformer in the query
Does NSSet *children = [parent children]; perform a fetch request?

Does NSSet *children = [parent children]; perform a fetch request?


By : pitter
Date : March 29 2020, 07:55 AM
To fix this issue It returns a Core Data internal 'faulting' set object that works like a set. When you access an item in the set, it will go to your persistent store for the data on first access. This is effectively indexed, so it will be faster than many fetch requests, and sometimes the relationship fault may have already fired, so it wouldn't go to the store at all.
Use the com.apple.CoreData.SQLDebug environment variable to figure out just what's going on under the hood and fine tune performance. Set it to 1 in your scheme.
Select Parent, Children, Children's Children, etc in single MySQL query

Select Parent, Children, Children's Children, etc in single MySQL query


By : Mohannad Bayoumi
Date : March 29 2020, 07:55 AM
will help you If you have a known limited depth, you can unroll the recursion and use a stored procedure or view. For MySQL, the following work:
Stored Routine solution:
code :
DELIMITER $$ 

CREATE PROCEDURE GetRelatedPersonsWithPersonId( IN pId VARCHAR(36)) 
        BEGIN 
                select * from Person where idPerson in ( 
                        select ParentId from ParentChildRelationship where ParentId = pId 
                        union 
                        select ChildID from ParentChildRelationship where ParentId = pId 
                        union 
                        select ChildID from ParentChildRelationship where ParentId in (select ChildID from ParentChildRelationship where ParentId = pId) 
                        union 
                        select ChildID from ParentChildRelationship where ParentId in (select ChildID from ParentChildRelationship where ParentId in (select ChildID from ParentChildRelationship where ParentId = pId)) 
                ) ; 

        END $$ 
Create view ChildRecurse 
As 
Select ParentId, ChildID from ParentChildRelationship 
Union 
Select x1.ParentId, x2.ChildId from ParentChildRelationship x1 
               Inner join ParentChildRelationship x2 on x2.ParentId = x1.ChildId 
Union 
Select x1.ParentId, x3.ChildId from ParentChildRelationship x1 
               Inner join ParentChildRelationship x2 on x2.ParentId = x1.ChildId 
               Inner join ParentChildRelationship x3 on x3.ParentId = x2.ChildId 
Union 
Select x1.ParentId, x4.ChildId from ParentChildRelationship x1 
               Inner join ParentChildRelationship x2 on x2.ParentId = x1.ChildId 
               Inner join ParentChildRelationship x3 on x3.ParentId = x2.ChildId 
               Inner join ParentChildRelationship x4 on x4.ParentId = x3.ChildId 
select * from person where idPerson=@ID or idPerson in (select ChildId from ChildRecurse where ParentId=@ID) 
Hibernate fetch parent and all children if any of children meet criteria

Hibernate fetch parent and all children if any of children meet criteria


By : Hùng Trần Quốc
Date : March 29 2020, 07:55 AM
around this issue I had to clear session. I dont need join 2nd time to pull all children since fetchtype is EAGER.
hibernate delete child from parent need fetch all children of parent?

hibernate delete child from parent need fetch all children of parent?


By : Adam Busch
Date : March 29 2020, 07:55 AM
wish helps you Hibernate has to fetch all the children in order to prepare proper SQL - needs to know IDs of children elements to delete. So there is no way to do it using ORM in way you would like to use it, but if you ask yourself a question, how would you do this in plain SQL obvious solution would be
DELETE c FROM child c WHERE c.parent_id=parentId
code :
Query q=session.createQuery(`DELETE c FROM chilc WHERE c.parent=:parent`);
q.setObject("parent",parent);
q.execute(); // q.executeUpdate?
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