Create a Social Media Backend

Go to the SAP Build lobby, and click Create

Select Build an Application.

Select Application Backend.

For the project name, enter Social Media Backend, then click Create.

Every time a user rates a single product, we want to store that as a single record in an entity.

1. In the Entities tab, click Create new.

   

   Set the entity title to Rating, and click Add.

2. Add the following fields to the entity:

   Field	Type
   Rating	Number
   RatedBy	Text
   ProductID	Text
   DateCreated	Date/time

   

3. Click Save App.

Every time a user adds a comment about a product, we want to store that as a single record in an entity.

1. In the Entities tab, click Create new.

   Set the entity title to Comment, and click Add.

2. Add the following fields to the entity:

   Field	Type
   Comment	Text
   ProductID	Text
   CommentedBy	Text
   DateCreated	Date/time

3. Click Save App.

We want to create a function that will aggregate the ratings of the products and return a single average rating for each product. If there are no ratings for a product, no record is returned for that product.

Functions are created using the standard SAP Build Apps formula, based on JavaScript syntax.

1. In the Functions tab, click Create new.

   Set the name to AverageRating, and click Create.

   

2. Click the + sign in the middle,then List records.

   

   Under Configuration, set the entity to Rating.

   

3. Click on Success (on the right).

   

   Click Output Value and name the output Ratings.

   Click Set Formula, and set the formula to the following:

   JavaScript

   Copy

   GROUP(outputs["Rating / Records listed"].records, item.productId, {productID: key, avg: AVERAGE(PLUCK(items,"rating")), count: COUNT(items) } )
   

   Click Save, and then click Add.

   

4. Click Save App.

What the formula does

The GROUP function takes our list of rating records, groups them by the product ID, and creates a new list with one element for each product ID.

The object for each product contains the product ID, the average rating for all the ratings for that product, and the number of ratings for that count.

Inputs

On the left, you can define inputs to the function, so the user could send a specific product ID and the calculations could be done only for that product..

In the Deployments tab, click Review and Deploy.

After reviewing the changes, click Deploy to Development.

It should take about a minute or two (going from Not deployed to Missing to Progressing to Healthy status). Once you see Healthy, you can add data to the entities and make calls from your front-end app. We will do this in the upcoming tutorials.