CODEWITHSUNDEEP
react-nativesubqueryrealm
learningtech
learningtech

Reputation: 33747

how to do subquery or backlink query in realm react-native?

The problem I'm trying to solve is this. If I have product, I'd like to know what other products I can purchase as a combination that's on-sale. If this were MySQL, I'd set up my tables and queries like so:

t_product: product_id, product_name
t_combination: combination_id, on_sale
t_product_combination: combination_id, product_id

// what other products should I buy along with my product_id == 1 to get a good deal?
SELECT product_id
FROM t_product
WHERE product_id IN (
    SELECT product_id
    FROM t_combination_product
    WHERE combination_id IN (
        SELECT combination_id
        FROM t_combination
        WHERE on_sale = 'yes'
        AND combination_id IN (SELECT combination_id FROM t_combination_product WHERE product_id = 1)
    )
)

I tried to do this in realm react-native as shown below:

I have two collections: Product and a Combination, set up as follows

class Product {};
Product.schema = {
    name: 'Product',
    primaryKey:'productId',
    properties: {
        productId:'int',
        product:'string'
    }
};

class Combination {};
Combination.schema = {
    name: 'Combination',
    properties: {
        onSale: {type: 'string'},
        products: {type: 'list',objectType:'Product'},
    }
};

What I want to do is given that I have Product.productId=1, I want to find all other products that belong to Combinations that have Combination.onSale='yes' and Product.productId IS IN (Combination.products ).

This is the query I tried to do in realm with react-native:

let queryFilter = "ANY Combination.onSale = 'yes' AND Combination.products = 1";
let data = realm.objects('Product').objectsWhere(queryFilter);

But when I run this, I get the error

undefined is not a function (evaluating 'realm.objects('Product').objectsWhere(queryFilter)')

If I remove the objectsWhere(queryFilter), then it just returns me the list of all Products that hasn't been filtered.

So it seems I'm using objectsWhere incorrectly? How do I fix this to find a list of all products that are onsale if purchased with product 1?

Upvotes: 0

Views: 624

Answers (1)

EpicPandaForce
EpicPandaForce

Reputation: 81588

If you had

class Product {};
  Product.schema = {
    name: 'Product',
    primaryKey:'productId',
    properties: {
        productId:'int',
        product:'string'
        combinations: {type: 'linkingObjects', objectType: 'Combination', property: 'products'}
    }
};

Backlink queries are not yet supported, so I think what you have to do is something like this:

let queryFilter = 'productId = 1';
let data = realm.objects('Product').filtered(queryFilter);
let combinations = data.combinations.filtered('onSale = true');
let linkedProducts = [];
for(let i = 0; i < combinations.length; i++) {
    linkedProducts.push(combinations[i]);
}
// linked products should contain what you need

Upvotes: 1

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