How do I get all rows from ITEM table, which are children of a parent ITEM table row, where relationship is stored separately? How can I do a join to do this? "get all rows from ITEM table, which are children of this specific ITEM table row, all child items from this parent item, where relationship is stored in separate RELATIONSHIP table"
So given there is an ITEMS and a RELATIONSHIPS table. The key columns are:
ITEMS
* ID
* << other columns>>
RELATIONSHIPS
* PARENT_ID
* CHILD_ID
I'm trying to understand whether the DataSet / DataRelation approach could somehow map these relations. For example if I basically want a way to implement the request "Give me all children ITEMS in a DataRow[] form, given a parent ITEM DataRow, based on the RELATIONSHIPS table", is there a way to do this using a DataRelation? Of if not what would be the easiest way to do this using the DataSet approach?
EDIT: That is, assuming I am using a DataSet, and within the DataSet I have one DataTable for each of the physical database tables I described above.
Thanks
Top of my head, you're looking for roughly this solution (and I'm not entirely certain if I understand your datastructure correctly):
SELECT child.othercolumns
FROM items AS child, relationships AS r, items AS parent
WHERE r.parent_id=parent.id AND r.child_id=child.id
Related
I have a "Parcel" Doctype
Which have a “Parcel Content” Doctype as a child table.
If i do:
frappe.get_doc('Parcel', 'NAME')
I get the object with the child table in it, it works for a single object.
But i need to get multiple objects with his child table fields.
So i can't render a custom jinja template.
eg:
frappe.get_all('Parcel', fields=['fields_of_parent', 'content'], filters=[])
So this will get me the filtered objects with the child table.
You have to query on the child table:
frappe.get_all("Parcel Content",
filters = dict(parent=parcel_name),
fields = [fields of child table])`
Use list comprehension:
[frappe.get_doc("Parcel", item.name).as_dict() for item in frappe.get_all("Parcel")]
This will return all doctypes with their respective child table items. Not even need to query based on child table name.
Sorry if this is a relatively easy problem to solve; I read the docs on inheritance and I'm still confused on how I would do this.
Let's say I have the parent table being car_model, which has the name of the car and some of it's features as the columns (e.g. car_name, car_description, car_year, etc). Basically a list of cars.
I have the child table being car_user, which has the column user_id.
Basically, I want to link a car to the car_user, so when I call
SELECT car_name FROM car_user WHERE user_id = "name", I could retrieve the car_name. I would need a linking component that links car_user to the car.
How would I do this?
I was thinking of doing something like having car_name column in car_user, so when I create a new data row in car_user, it could link the 2 together.
What's the best way to solve this problem?
Inheritance is something completely different. You should read about foreign keys and joins.
If one user drives only one car, but many users can drive same car, you need to build one-to-many -relation. Add car_name to your user table and JOIN using that field.
For an assessment task I'm doing, an entity album has the attribute also_bought, which is a self-referential attribute. However, this one attribute has multiple entries for any one album - as the also_bought recommendations are rarely only one recommendation - and thus, is a bit of a question mark when it comes to normalisation. I'm not sure whether it passes 1NF or not.
To be clear, the entire entity's set is
Album(album_id, title, playtime, genre, release_date, price, also_bought)
"Also bought" items should be stored in a separate table, something like.
AlsoBought (table)
album_id
also_bought_album_id
Then configure foreign keys from both columns to reference Album.album_id.
You mean that Album is a "self-referencing table" because it has a FK (foreign key) from one column list to another in the same table? (A FK constraint holds when subrow values for a column list must appear elsewhere.) If you mean that the type of also_bought is a list of album_ids, there is no FK from the former to the latter, because values for the former (lists of ids) are not values for the latter (ids). There's a constraint that is reminding you of a FK.
Anyway, normalization is done to one table, and doesn't depend on FKs.
But any time you are "normalizing to 1NF" eliminating "non-atomic columns" you have to start by deciding what your "table" "columns" contain. If you decide a cell for a column in a row contains "many values" then you don't have a relational table and you have to come up with one. The easiest way is to assume a set-valued column to get a relation and then follow the standard rules for elimination of too-complex column types.
so the story is very simple.
I have one table called Products and another Called categories. In addition, i have another table called ProductCategories that hold the relationship of catetories to their corresponding products (i.e, the table has two columns, ProductId, ColumnId).
For some reason, after adding all those table to my entity model, i don't have "Access" to it, hence i can do myentityModel.ProductCategories, so i could relational items between those two tables.
And yes, the ProductCategores table is added as "Association" to the entity model. i don't really understand that.
EDIT:
I do see that as part of creating new "Product" i can pass EntityCollection of "Category". So i do query from my entity model for a list of the matching categories that the user selected (on the webpage). so for example, i get (after query the model), an Objectset of "Category". However, i encountered two issues:
the 'AddObject' accept only EntityCollection, hence i need to re-create a set and then add all the objects from the ObjectSet to the entityCollection, in this process i need to detach it from the previous model and add it to the new collection. if not, i get an exception.
when i do the SaveChanges, i see that i get an exception that it was actually trying to Create new Category rather than adding new ProductCategory. again, am i missing something here?
Thanks.
This sounds like a Many-to-Many relationship. In your entity model, you don't need to declare the join table as a separate entity. Instead, you configure the relationship between the Products and the Categories as a Many-to-Many and add metadata about the join table. In Hibernate, you would have:
#ManyToMany(targetEntity=Categories.class, cascade={CascadeType.ALL}, fetch = FetchType.LAZY)
#JoinTable(name="tb_products_categories",
joinColumns=#JoinColumn(name="category_id"),
inverseJoinColumns=#JoinColumn(name="product_id")
)
#IndexColumn(name="join_id")
public List<Categories> getCategories() {
return categories;
}
When you query, the ORM layer takes care of determining SQL and traversing table joins.
i have a many to many table relationship that involves 2 logical tables.
Record table that joins to a relation table on primaryID
Second instance of record table that joins to the relation table on ReciprocalID
The purpose of this is to show family relations within the database. Each primary Record table has one or more rows in the relationtable that shows everyother family relationship this person has in the database.
I have been tasked with trying to make a contact list that involves displaying the names of each of the children that attend this school along with their parents and contact information.
I have gotten to a point where I am able to show the children under each parent, but now I have to find a way to merge these together.
Since I have no control over the design of this database(its Education Edge 7) I have made a separate database that holds my queries and views for my reports. The school I am doing this work for only has access to CR 8.5.
Right now I have my top group in CR as the lastname of the recordstable, my second group is on the fullname of the recordstable. I have a subreport that pulls in all the child records.
I have used a case when statement in my primary view(the one described above) to convert 'daughter' and 'son' to child and 'mother' or 'father' to parent.
hopefully this hasnt rambled too much. If you need anymore information just ask.
SELECT dbo.vwEA7RelationshipsTableView.PRIMARYID,
dbo.vwEA7RecordsTableView.LASTNAME AS PRIMARYLASTNAME,
dbo.vwEA7RecordsTableView.FIRSTNAME AS PRIMARYFIRSTNAME,
dbo.vwEA7RecordsTableView.NAMEFORDISPLAY AS PRIMARYNAME,
CASE dbo.vwEA7RelationshipsTableView.PRIMARYDESC
WHEN 'Father' THEN 'Parent'
WHEN 'Mother' THEN 'Parent'
WHEN 'Son' THEN 'Child'
WHEN'Daughter' THEN 'Child'
ELSE dbo.vwEA7RelationshipsTableView.PRIMARYDESC
END AS PRIMARYDESC,
dbo.vwEA7RelationshipsTableView.RELATIONID,
vwEA7RecordsTableView_1.LASTNAME AS RELATIONLASTNAME,
vwEA7RecordsTableView_1.NAMEFORDISPLAY AS RELATIONNAME,
dbo.vwEA7RelationshipsTableView.RELATIONDESC
FROM dbo.vwEA7RelationshipsTableView INNER JOIN
dbo.vwEA7RecordsTableView ON
dbo.vwEA7RelationshipsTableView.PRIMARYID = dbo.vwEA7RecordsTableView.ID INNER JOIN
dbo.vwEA7RecordsTableView AS vwEA7RecordsTableView_1 ON
dbo.vwEA7RelationshipsTableView.RELATIONID = vwEA7RecordsTableView_1.ID
TableViews are really just recreation of the primary tables from the main database.
I have solved this issue. My sql code was good, it was a matter of formatting my internal paramaters for Crystal as well as some creative grouping.