I have a design problem with SQL request:
I need to return data looking like:
listChannels:
-idChannel
name
listItems:
-data
-data
-idChannel
name
listItems:
-data
-data
The solution I have now is to send a first request:
*"SELECT * FROM Channel WHERE idUser = ..."*
and then in the loop fetching the result, I send for each raw another request to feel the nested list:
"SELECT data FROM Item WHERE idChannel = ..."
It's going to kill the app and obviously not the way to go.
I know how to use the join keyword, but it's not exactly what I want as it would return a row for each data of each listChannels with all the information of the channels.
How to solve this common problem in a clean and efficient way ?
The "SQL" way of doing this produces of table with columns idchannel, channelname, and the columns for item.
select c.idchannel, c.channelname, i.data
from channel c join
item i
on c.idchannel = i.idchannel
order by c.idchannel, i.item;
Remember that a SQL query returns a result set in the form of a table. That means that all the rows have the same columns. If you want a list of columns, then you can do an aggregation and put the items in a list:
select c.idchannel, c.channelname, group_concat(i.data) as items
from channel c join
item i
on c.idchannel = i.idchannel
group by c.idchannel, c.channelname;
The above uses MySQL syntax, but most databases support similar functionality.
SQL is made for accessing two-dimensional data tables. (There are more possibilities, but they are very complex and maybe not standardized)
So the best way to solve your problem is to use multiple requests. Please also consider using transactions, if possible.
Related
I am implementing multi tenancy using single database and separating data for each tenant using a tenant_id. This id is passed in the jwt token as well. I have two tables right now genre and books. genre table has columns like
tenant_id, genre_id, ..... and books table has columns genre_id, book_id, book_name, ....
So 1 genre can have multiple books associated with it and 1 tenant can have multiple genres associated with it.
Now every time a book is fetched or updated I want to make sure the right person is making these calls.
I know of two ways to do it.
First way:
Make two queries. First fetch the book, get the associated genre_id in the object. Then fetch that genre and compare the jwt tenant_id with the tenant_id inside this genre object.
Something like this
const book= await ReadBook(req.query.book_id); // fetches my book from db
const genre = await ReadBook(book.genre_id); // fetches the genre from db
if (genre.tenant_id === jwtToken.tenant_id) {..} // compare if same or not
Second way:
Do this query in db
select b.*, g.tenant_id as tenant_id
from book_data b, genre_data g
where b.book_id = '0eokdpz0l' and g.tenant_id = 'M1MzgzMDM' and b.genre_id = g.genre_id
Which method is more efficient?
If theres a more efficient method then these then please let me know too
It's good practice to stick to ORM abstraction if possible, while minimising how much and how often data is transferred to/from db. Sequelize is able to construct an equivalent to that query for you, with the necessary joins and filters on the ids. Something among the lines of:
Books.findAll({
where: {book_id: '0eokdpz0l'},
include: [{
model: Genre,
where: {tenant_id : jwtToken.tenant_id}
}]
}).then(books => {
/* ... */
});
Running multiple queries in sequence not only adds latency due to additional round trips to/from db (and possibly connection setup if you're not pooling or holding them open) but it's also moving more bytes of data around, needlessly. tenant_id mismatch on db would send back a shorter message with an empty result. Checking it on client side requires downloading data even when you'll have to discard it.
I have a model called lists, which has a column called item_ids. item_ids is a JSON column (MySQL) and the column contains array of UUIDs, each referring to one item.
Now when someone creates a new list, I need to search whether there is an existing list with same set of UUIDs, and I want to do this search using query itself for faster response. Also use ActiveRecord querying as much as possible.
How do i achieve this?
item_ids = ["11E85378-CFE8-39F8-89DC-7086913CFD4B", "11E85354-304C-0664-9E81-0A281BE2CA42"]
v = List.new(item_ids: item_ids)
v.save!
Now, how do I check whether a list exists which has item ids exactly matches with that mentioned in query ? Following wont work.
list_count = List.where(item_ids: item_ids).count
Edit 1
List.where("JSON_CONTAINS(item_ids, ?) ", item_ids.to_json).count
This statement works, but it counts even if only one of the item matches. Looking for exact number of items.
Edit 2
List.where("JSON_CONTAINS( item_ids, ?) and JSON_LENGTH(item_ids) = ?", item_ids.to_json, item_ids.size).count
Looks like this is working
You can implement a has many relation between lists and items and then access like this.
List.includes(:item).where('items.id in (?)',item_ids)
To implement has_many relation:
http://guides.rubyonrails.org/association_basics.html#the-has-many-through-association
I am struggling with a basic problem. i am using cake php 2.5. i try to apply the find query in the company model and receiving all the data from companies and with its associations, but i only want to receive the data from company table and want to exclude the data from rest of relationships, can anyone help me with this. below are my queries.
$this->loadModel('Company');
$fields=array('id','name','logo','status');
$conditions=array('status'=>1);
$search_companies = $this->Company->find('first',
compact(array('conditions'=>$conditions,'fields'=>$fields)));
print_r($search_companies);die();
echo json_encode($search_companies);die();
With out seeing your data output, I am just going to take a stab at the problem.
Inside your $search_companies variable you are getting a multidimensional array probably with the other values of the other tables.
Why not just select the one array:
$wantedData = $search_companies['Company'];
// The key Company (which is the model) should be the data you are wanting.
Try setting model's recursive value to -1
$this->Company->recursive = -1;
$search_companies = $this->Company->find('first',
compact(array('conditions'=>$conditions,'fields'=>$fields)));
With this you will not fire the joins queries and therefore you only retrieve model's information.
Cakephp provide this functionality that we can unblind few/all associations on a any model. the keyword unbindModel is used for this purpose. inside the unblindModel you can define the association type and model(s) name that you want to unblind for that specific association.
$this->CurrentModelName->unbindModel(array('AssociationName' => array('ModelName_Youwwant_unblind')));
I have a database setup as follows (unfortunatelly was not allowed to publish diagram image in here so need to describe:
Responses table - contain RespondentID, QuestionID, ResponseOptionID
ResponseProperties - contain ResponsePropertyID, ResponsePropertyTypeID, Name
ResponsePropertyTypes - contain ResponsePropertyTypeID, Name
ResponsesInProperties (a many to many table) - contains ResponseID, ResponsePropertyID
There is a many to many relationship on ResponsesInProperties table. This table does not show in EF of course.
Say I have two response property types "Country" and "Wave" and corresponding ResponeProperties "USA", "UK" and "Wave2011", "Wave2012".
Now I need to get back from the database all (and not duplicated) responses that would be in USA and also in Wave2012. The trick is that every response I need must be in both Wave2012 and USA. I am trying to achieve this with LINQ to SQL. The below is Linq I came up with that get's me the correct records but they appear many times for different properties. Limiting the properties gives me no records whatsoever....
Any help appreciated!
var responses = from r in db.Responses
from rp in r.ResponseProperties
select new
{
RespondentID = r.RespondentID,
QuestionCode = r.Question.Code,
ResponseOptionCode = r.ResponseOption.Code,
ResponseOptionCodeName = r.ResponseOption.Text,
ResponsePropertyName = rp.Name,
ResponsePropertyTypeName = rp.ResponsePropertyType.Name
};
To clarify, you are trying to do this with LINQ to SQL and not EF as they have rather different models for M-M. With LINQ to SQL, you do have to include the middle join table.
The key thing missing from your query at this point is the filter (Where) clauses. You need to specify them for both sides of the join to properly filter the results. You indicate that when you supply a filter you get back no records. Can you clarify your question with that filter as it may help to fix your underlying problem.
Your query cannot produce unique responses because you also get ResponsePropertyName and ResponsePropertyTypeName, which will duplicate the results.
This entity framework query -
from r in db.Responses
where r.ResponseProperties.Any (rp => rp.Name == "USA")
where r.ResponseProperties.Any (rp => rp.Name == "Wave2012")
select new
{
RespondentID = r.RespondentID,
QuestionCode = r.Question.Code,
ResponseOptionCode = r.ResponseOption.Code,
ResponseOptionCodeName = r.ResponseOption.Text,
};
does produce unique Responses that are in USA and in Wave2012. The produced sql will show two EXISTS predicates with AND.
I am using SQL Alchemy and I want to return a list of Document Ids. The Ids are the primary key in the documents table. My current query returns a list of tuples.
userDocs = session.query(Document.idDocument).filter(Document.User_idUser == user.idUser).all()
The reason I want a list of ids is so that I can search another table using in_(userDocs).
So another solution would be to be able to search using tuples. I am currently returning nothing from my second query using userDocs.
Thank you!!
You don't need to do an intermediate query, you can do this all in one shot!
things = session.query(Things) \
.join(Thing.documents) \
.filter(Document.User_idUser==user.idUser)
You just query on the properties of the Document through its relationship() on the intended entity.