Fetching same vertex data for multiple levels in orientdb - orientdb

Question

I am a beginner in OrientDB.
Consider that I have 2 Vertex, Cat and Val.
Cat contains a property called category and Val contains a property called value.
Categories can have sub-categories and those can further have sub-categories and so on. The categories and sub-categories are stored in Vertex Cat. The sub-categories are mapped using an edge called CatEdge whose from and to are the same vertex i.e. Cat.
For example, consider a category 'Education' which has two sub-categories 'School' and 'College'. The 'College' sub-category has further sub-categories 'Bachelors' and 'Masters'. So, there will be an edge in CatEdge from 'Education' to 'School' and 'College', and from 'College' to 'Bachelors' and 'Masters'.
Education
|- School
|- College
|- Bachelors
|- Masters
Apart from these, the Cat Vertex can have categories that do not have any sub-categories, for example 'FirstName', 'LastName', etc.
All the 'leaf' categories (that do not have further sub-category) have an edge called ValEdge from Vertex Cat to Vertex Val.
I want to retrieve all 'value' from Val for all the categories and sub-categories.
What I have done:
First, I fired the following query to retrieve all categories that do not have sub-categories and which are not a sub-category of other category:
select from Cat where #rid not in (select #rid, expand(both('CatEdge')) from Cat)
Then, programatically, I loop through all the categories fetched and find their corresponding values:
select expand(out('ValEdge')) from Cat where category = 'FirstName'
Second, I fetch all the categories that have sub-categories or are itself a sub-category using:
select from (traverse out('CatEdge') from Cat) where out('CatEdge').size() > 0
And store it in a list called SubList.
The above query will give me 'Education' and 'College'.
Using this list, for each item, I check if there exists its sub-category using:
select expand(out('CatEdge')) from Cat where category = 'Education'
The above query will give 'School' and 'College'. Then, programmatically, I check if 'School' and 'College' exists in SubList.
If it exists, I first remove it from the SubList and fire the above query again and this continues until I get zero rows.
If it does not exists in SubList, then it is a 'leaf' category and then find its value in the Val Vertex.
As you may have noticed, this is getting too complex. Is there any other way that I can achieve the same?

Answer 1

If this is your situation:
create class Cat extends V
create property Cat.category string
create class CatEdge extends E
create class Val extends V
create property Val.value integer
create class ValEdge extends E
create vertex Cat set category = 'Education'
create vertex Cat set category = 'School'
create vertex Cat set category = 'College'
create vertex Cat set category = 'Bachelors'
create vertex Cat set category = 'Masters'
create vertex Val set value = 1
create vertex Val set value = 2
create vertex Val set value = 3
create edge CatEdge from (select from Cat where category = 'Education') to (select from Cat where category = 'School')
create edge CatEdge from (select from Cat where category = 'Education') to (select from Cat where category = 'College')
create edge CatEdge from (select from Cat where category = 'College') to (select from Cat where category = 'Bachelors')
create edge CatEdge from (select from Cat where category = 'College') to (select from Cat where category = 'Masters')
create edge ValEdge from (select from Cat where category = 'School') to (select from Val where value = 1)
create edge ValEdge from (select from Cat where category = 'Bachelors') to (select from Val where value = 2)
create edge ValEdge from (select from Cat where category = 'Masters') to (select from Val where value = 3)
And if I understood your intention correctly, this query will work:
select in("ValEdge").category, value from Val
Output:
UPDATE
select category, $subcategories, $value from Cat
let
$subcategories = ( select category from (traverse out('CatEdge') from $parent.$current ) where $depth >=1 ),
$value = ( select out('ValEdge').value as value from $current )
returns this JSON.
Note that for all categories, or you have a list of subcategories, or, if it's a leaf, its value.