In exercise 03 you deployed the service definition (including the referenced data model) to a SQLite-powered persistence layer. While at this stage the OData service is working nicely, we don't yet have data to explore with.
In this exercise you'll seed the persistence layer with data from CSV files, which is often a great way to kick start exploration, development and testing in the early stages of a project.
After completing these steps you'll have some authors and books data in your OData service and will have explored that data in the browser with OData Query operations.
The SAP Cloud Application Programming Model adopts a "convention over configuration" approach in many areas, one of which is the automatic recognition and loading of data from CSV files during a deployment. In this step you'll create a csv/ directory within the db/ directory, add two CSV files (one for each of the entities) and redeploy. The deployment process will spot the CSV files and load the contents into the tables in the persistence layer.
👉 Create a csv/ directory within the db/ directory, and copy into it the CSV files (from this repository) my.bookshop-Books.csv and my.bookshop-Authors.csv. Use the "Raw" link from within each of these GitHub resources to get the actual CSV data to download (and don't forget to ensure the .csv extension is used for the files that you save).
Your directory structure should then look something like this (the screenshot also shows the content of the two CSV files):
The CSV files are discovered and used during a cds deploy, so a new deployment is required. While the cds watch will restart the service, it won't do a deploy for us, so we'll do that manually now.
👉 Deploy again, this time noting that you don't have to specify the --to option:
user@host:~/bookshop
=> cds deployDuring deployment this time you should see extra messages:
> filling my.bookshop.Authors from db/csv/my.bookshop-Authors.csv
> filling my.bookshop.Books from db/csv/my.bookshop-Books.csv
/> successfully deployed to ./bookshop.db
👉 Now the data's been loaded, you should fire up cds watch again:
user@host:~/bookshop
=> cds watchNow the Books and Authors entitysets in the OData service will show data in response to OData Query and Read operations.
The OData standard describes a number of different operations - Create, Read, Update, Delete and Query (otherwise known as 'CRUD+Q'). With your browser you can try out Read and Query operations directly.
👉 Try out a few Read and Query operations on the data in the service like this:
| Read / Query | URL |
|---|---|
| Show all books | http://localhost:4004/catalog/Books |
| Show all authors | http://localhost:4004/catalog/Authors |
| Retrieve book with ID 421 | http://localhost:4004/catalog/Books(421) |
| Retrieve author with ID 42 and also their books | http://localhost:4004/catalog/Authors(42)?$expand=books |
Your OData service now has sample data that you can access via OData operations.
- Does the order of the fields defined in the CSV files have to match the order of the properties defined in the entities in the data model?
- Where do you think the format of the CSV file names has come from?
- How come we didn't have to specify the details (in
--to) during the deployment in this exercise?