05 / 06Intermediate

Blockchain components

Navigate to the blockchain folder

shell

cd rell/src

The key components of the blockchain dapp

The pagination utility comes from the FT4 library, so you need to import it first.

./chromia.yml

libs:  ft4:    registry: https://gitlab.com/chromaway/ft4-lib.git    path: rell/src/lib/ft4    tagOrBranch: v1.2.0r    rid: x"E96915FD7C9A5DD4E183D86F4A5B4BB5083A7CC1EDEB1465EDFFC926E67C93F6"    insecure: false

You store the data to be analyzed in an entity called product. Its structure works much like a table in a relational database.

./main.rell

entity product {    name: text;    description: text;    quantity: integer;    price: integer;}

To populate the data, you use an operation called seed_data, which builds a list of products. It creates all the entities in a single batch with the statement create product (batch);.

./main.rell

operation seed_data() {    // 100 bytes    val name = "UltraPure Hydro Flask ProMax: Advanced Insulated Stainless Steel Bottle for Active and Everyday Use.";    // 500 bytes    val description = "Introducing the EcoSmart Water Bottle – your ultimate hydration companion! Made from premium, BPA-free materials, this bottle is designed for both functionality and style. With double-wall insulation, it keeps your beverages icy cold for up to 24 hours or piping hot for up to 12 hours. Its sleek, ergonomic design fits perfectly in your hand or cup holder. Featuring a leak-proof lid and a wide  mouth for easy cleaning or adding ice cubes, it’s perfect for gym sessions, hikes, or daily  commutes. Stay refreshed and eco-friendly with EcoSmart!";    // in total a size of 1 object is going to be 616 bytes    val batch_amount = 10; // amount of batches created    val batch_size = 10000; // the batch will have this number of entities to be created as a batch    // total data size can be calculated     // total_size = batch_amount * batch_size * object_size    // the  total size can be tuned with changing any parameter listed above.    var batch = list<struct<product>>();    for (x in range(batch_amount)) {        val shift_index = x * batch_size;        for (y in range(batch_size)) {            batch.add(                struct<product>(                    name = name + shift_index + y,                    description = description,                    quantity = shift_index + y,                    price = shift_index + y                )            );        }        create product ( batch );        batch.clear();        print("saved", x);          }}

To read the products back from the node one page at a time, you call the query get_products_paginated. It relies on the cursor-based pagination provided by FT4.

./main.rell

 query get_products_paginated(page_size: integer?, page_cursor: text?): paginator.paged_result {    val before_rowid = paginator.before_rowid(page_cursor);    val paginated_result = product @* {        .rowid > (before_rowid ?: rowid(0))    } (        paginator.pagination_result(            data = map_product($).to_gtv_pretty(),            rowid = .rowid        )    ) limit paginator.fetch_data_size(page_size);    return paginator.make_page(paginated_result, page_size);}

Data model

code

product {    name: text;    description: text;    quantity: integer;    price: integer;}

Written for this site from Chromia’s public course. Code samples are the course’s own.