Demo API Sample

The Demo API is a representative sample application that illustrates basic concepts. This API sample demonstrates how you can build and run modern systems for web/mobile applications data access or for data integration using .

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The

Demo

API is a representative sample application that illustrates basic

Layer7 Live API Creator

concepts. This API sample demonstrates how you can build and run modern systems for web/mobile applications data access or for data integration using

Layer7 Live API Creator

The

Demo

API sample is included with the single-user demonstration package of

Layer7 Live API Creator

that is based on Jetty and with the

Layer7 Live API Creator

Docker container installation. No additional steps are required to load this API.

You can also load this API sample if you have installed

Layer7 Live API Creator

on another Java container.

In this article:

Problem: Servers are Hard to Build, Particularly the Business Logic

REST/JSON servers are the accepted approach for mobile application access to integrated data. In a Java stack, you might need to use Jersey, Jackson, and/or Java Persistence API (JPA). These frameworks can reduce coding, but they are complex to build and time-consuming, particularly when you consider enterprise-class requirements like filtering, sorting, pagination, and optimistic locking.

And, adding business logic and security can add significant effort to your development. For example, you might want to check credit,
not just for placing orders, but all the other user stories (such as change item, delete item, re-select product). The business logic requirements–expressed in the following five lines–are clear to IT and business users alike, yet require hundreds of lines of code to implement:

Validate balance < credit-limit, where

Balance is derived as the sum of the unpaid order amounts, where

Order amounts are the sum of Item amounts, where

Item amounts are a discounted price * quantity, where

Prices are obtained from Products

The following sections describe how to build REST APIs in

Layer7 Live API Creator

. This API provides a user interface (UI) that:

Accepts spreadsheet-like expressions that express what your data means, how it is computed, validated, including actions such as auditing and deep copy.

Executes this spreadsheet-like logic on all RESTful update requests (PUT, POST, and DELETE).

Watch the Video

The following video demonstrates of how to build a simple REST API in under five minutes that would otherwise require weeks. The REST API accepts orders from partners, mobile applications, or web applications; processes the orders and the related requirements to change orders; and posts messages to specific suppliers' systems.

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Database Schema

The following image shows the schema for the

Demo

API sample:

Solution

The sample solution uses a familiar problem–customer, PurchaseOrder, and LineItems–to introduce various concepts in

Layer7 Live API Creator

Expose database tables as REST resources.

Declare your business logic.

Define the security for your API.

Provide a UI to access your data using the defined APIs using Data Explorer.

For more information about Data Explorer, see Data Explorer.

You can also build a UI using JavaScript/HTML5. For more information, see the JavaScript Sample Application.

Expose Database Entities as REST Resources

To build a REST server, create an API and connect to your database using API Creator, which automates the web service layer and data access.

Layer7 Live API Creator

automatically exposes the entities (tables and views) and stored procedures as REST endpoints. You can test the entities and stored procedures in the REST Lab without writing a program.

For more information:

About how to connect your API to your database, see Database Connectivity.

About the system REST endpoints

Layer7 Live API Creator

exposes, see System REST Endpoints.

About how to test entities and stored procedures in the REST Lab, see Test your API Using the REST Lab.

Customize Multi-Table Resources

You can present related data within a single request by creating table-based resources. The following image shows related tables for the

Demo

API in API Creator:

You can:

Define multi-level, table-based resources that deliver this data in a single JSON response, thereby minimizing the latency for your API. API Creator defaults the sub-resource join (Customers/Orders) from the foreign key validations.

For more information about how to create table-based resources, see Define Table-Based Resource Types.

Shape your API by specifying aliases for the attributes that are returned to the client.

Define JavaScript resources by using your own code.

Test your resources using the REST Lab.

Automation includes support for enterprise-class level services such as pagination, optimistic locking, and change summary information for client refresh.

For more information:

About pagination, see GET.

About optimistic locking and changing summary information, see PUT.

Business Logic Must be Addressed

The real work involves the business logic. Consider the Place Order user story or requirement. You might need to implement business logic for requirements such as the following:

Check credit limit.

Ensure that the balance cannot exceed the credit limit.

Implement the logic for the balance, which is the sum of the unpaid purchase order totals.

Implement the logic for the purchase order total, which is the sum of the Line Item amounts.

Implement the line item amount as the derivation of quantity times the part's price.

Following that, you must identify the related use cases that must also adhere these rules. You must then design these rules for change detection, change propagation to dependent data, and optimization. Soon, the simple five-line specification becomes 500 lines of code. And yet, the requirements, as illustrated with the venerable cocktail napkin, were so simple. If only the requirements were executable.

Declare your Business Logic

Business logic requires domain-specific code, which can take up to approximately 500 lines of code. Writing the code can require weeks of work to build and test the dependencies. That is not fast, and it is not simple. What if, instead of programming your server for each use case/dependency, you could simply enter the requirements from the cocktail napkin? Entering the requirements from the cocktail napkin would be simple and fast in

Layer7 Live API Creator

You can chain multi-table derivation logic, such as the customers' balance, use them in related logic. The

Check Credit

topic groups five rules in the

Demo

API. The validation rule on the customer's balance (see

demo:Customer

table) enforces the credit limit check, which in turn uses the the purchase order's

amount_total

result to compute the customer's

balance

Layer7 Live API Creator

eliminates and simplifies SQL access by optimizing the derivations.

For more information about exploring logic, see Logic.

Define the Security for your API

To secure your API, you require fine-grained security down to the row and column instance. You can define one or more roles for a user. You can associate roles data rows in your database and can use their column values to filter queries against other tables.

The following image shows the

My Orders - no update of paid flag

entity permission for the

PurchaseOrder

table:

Screen Shot 2018-05-17 at 3.06.46 PM.png

Define Table-Based Permissions

You can filter orders for a sales rep role to only return the purchase orders that are assigned to them, without the ability to alter the paid flag.

For more information about how to set entity-level permissions for roles, see Authorization and Role-Based Endpoint Access.

Define Row Filtering Based on User Table Value using Global

The

employee

object has a unique key on

employee_id

. In this example, we want to use the employee values to filter rows in other tables. In this example, we want to filter

purchaseorders

whose

salesep_id

matches the

employee_id

of the currently logged in employee.

You define a a global (

current_employee_row

) for the

SalesRep

role to obtain the currently logged in employee row. The predicate refers to the global using the

@{<globalName>.<globalAttribute>}

syntax. When an API user assigned the

SalesRep

role accesses the predicate,

Layer7 Live API Creator

merges the global into the resources that are defined for

Purchase Order

table.

Define Column Access Permissions

You can define the columns that the user role can access by adding a table permission. The

My Orders Write

entity permission specifies the permitted columns for updates, omitting the

paid

column, on the Entity Permissions
tab:

Screen Shot 2018-05-17 at 3.08.28 PM.png

For more information about how to define roles for an API user, see Authorization and Role-Based Endpoint Access.

Observations

The Demo API sample illustrates the following:

You did not write any code for request handling, database access, or business logic. If necessary, you can write code to extend the logic using server-side JavaScript and scale it to complexity (for example, a Bill of Materials explosion with four rules).

For more information about how logic scales to complexity, see the Logic Tutorial.

You solved all the use cases, even though you targeted only Add Order.

Layer7 Live API Creator

reuses the logic.

For more information about re-use, see Logic.

The logic is unordered.

Layer7 Live API Creator

takes care of the order through logic-dependency analysis.

Layer7 Live API Creator

repeats the analysis on every change, prunes your logic based on actual changes, and SQLs are eliminated/optimized to reduce server traffic. As for ordering, these optimizations are repeated on each change.

For more information about how

Layer7 Live API Creator

does not optimize your logic, see Performance.

Advanced Topic: Approaches to Creating Resources

The

Demo

API sample includes examples that demonstrate multi-database resources that are created using various approaches to creating resources and that highlight the advantages of using the declarative approach. These examples reference the

Sample

API as the other database resource.

The

Sample

API is included with the single-user demonstration package of

Layer7 Live API Creator

that is based on Jetty and with the

Layer7 Live API Creator

Docker container installation.

For more information about the

Sample

API, see the Sample Database.

Create Resources using the Declarative Approach

You can extend the declarative approach to creating table-based resources to represent data from multiple databases, joined using a virtual relationship that you define in API Creator. The

CustomerOrders_Declarative

resource demonstrates a multi-database resource between the

demo:customer

table and the

sample:orders

table in another database. This resource is created using a declarative approach without
any code written.

Use this approach when you are connecting to a data source. This approach requires the least effort than the other approaches while providing full services for filtering, pagination, and update from

Layer7 Live API Creator

The following image shows the

CustomerOrders_Declarative

resource, the

CustomerOrders_JS_SubResource

resource, and the

CustomerOrders_JS_Totally

resource in the

Demo

API sample:

To view the virtual relationship, with the API open, in the Create section, click Schema
. The Tables tab displays by default. Click the

demo:customer

table from the list of tables. View the virtual to-children relationships that are displayed in the Relationships to Children list.

For more information about how to access the virtual relationships, see Manage Relationships.

Create Resources using the Combined Approach (Declarative and Code-Based)

The

CustomerOrders_JS_SubResource

resource demonstrates a combination of declarative and code-based approach to creating resources. With this approach, the parent resource is a table-based resource for the

demo:customer

table, joined with another sub-resource using the

CustomerOrders_JS_SubResource

JavaScript resource. This approach makes a SQL call for customers, and then makes a REST call to the

sample:orders

REST endpoint that is connected to a different database using the

Sample

API. The combined resource is a compound document resource with approximately 10-12 lines of code that is written in the JavaScript resource. This approach includes minimal services.

Use this approach when you need to define code to integrate data from cloud-based data sources.

For more information about how to define resources between databases, see Define Table-Based Resource Types.

Create Resources using the Code-Based Approach

The

CustomerOrders_JS_Totally

resource demonstrates the code-based approach to creating resources. With this approach, you define the code that orchestrates data from different sources (customers from the

Demo

API and orders from the

Sample

API). This JavaScript resource requires about 50 lines of code. This approach includes minimal services for filtering. It does not provide services for pagination and update.

Use this approach when you require the flexibility to integrate an arbitrary source of data.

Tutorials and Samples

Layer7 Live API Creator 5.4

Demo API Sample