JSON Interface – examples

We have several ways of using the JSON interfaces. I will give few examples with the required C/AL code. I will be using Advania’s Online Banking solution interfaces for examples.

The Advania’s Online Banking solution is split into several different modules. The main module has the general framework. Then we have communication modules and functionality modules.

On/Off Question

A communication module should not work if the general framework does not exist or is not enabled for the current company. Hence, I need to ask the On/Off question

This is triggered by calling the solution enabled Codeunit.

The interface function will search for the Codeunit, check for execution permissions and call the Codeunit with an empty request BLOB.

The “Enabled” Codeunit must respond with a “Success” variable of true or false.

The “Enabled” Codeunit will test for Setup table read permission and if the “Enabled” flag has been set in the default record.

This is how we can make sure that a module is installed and enabled before we start using it or any of the dependent modules.

Table Access Interface

The main module has a standard response table. We map some of the communication responses to this table via Data Exchange Definition. From other modules we like to be able to read the response from the response table.

The response table uses a GUID value for a primary key and has an integer field for the “Data Exchange Entry No.”. From the sub module we ask if a response exists for the current “Data Exchange Entry No.” by calling the interface.

The Interface Codeunit for the response table will filter on the “Data Exchange Entry No.” and return the RecordID for that record if found.

If the response is found we can ask for the value of any field from that record by calling

Processing Interface

Some processes can be both automatically and manually executed. For manual execution we like to display a request page on a Report. On that request page we can ask for variables, settings and verify before executing the process.

For automatic processing we have default settings and logic to find the correct variables before starting the process. And since one module should be able to start a process in the other then we use the JSON interface pattern for the processing Codeunit.

We also like to include the “Method” variable to add flexibility to the interface. Even if there is only one method in the current implementation.

Reading through the code above we can see that we are also using the JSON interface to pass settings to the Data Exchange Framework. We put the JSON configuration into the “Table Filters” BLOB field in the Data Exchange where we can use it later in the data processing.

From the Report we start the process using the JSON interface.

The ExecuteInterfaceCodeunitIfExists will also verify that the Interface Codeunit exists and also verify the permissions before executing.

Extensible Interface

For some tasks it might be simple to have a single endpoint (Interface Codeunit) for multiple functionality. This can be achieved by combining Events and Interfaces.

We start by reading the required parameters from the JSON and then we raise an event for anyone to respond to the request.

We can also pass the JSON Interface Codeunit, as that will contain the full JSON and will contain the full JSON for the response.

One of the subscribers could look like this

Registration Interface

This pattern is similar to the discovery pattern, where an Event is raised to register possible modules into a temporary table. Example of that is the “OnRegisterServiceConnection” event in Table 1400, Service Connection.

Since we can’t have Event Subscriber in one module listening to an Event Publisher in another, without having compile dependencies, we have come up with a different solution.

We register functionality from the functionality module and the list of modules in stored in a database table. The table uses a GUID and the Language ID for a primary key, and then the view is filtered by the Language ID to only show one entry for each module.

This pattern gives me a list of possible modules for that given functionality. I can open the Setup Page for that module and I can execute the Interface Codeunit for that module as well. Both the Setup Page ID and the Interface Codeunit ID are object names.

The registration interface uses the Method variable to select the functionality. It can either register a new module or it can execute the method in the modules.

In the “ExecuteMethodInApps” function I use the filters to make sure to only execute each Interface Codeunit once.

The registration is executed from the Setup & Configuration in the other module.

Extend functionality using the Registered Modules.

As we have been taught we should open our functionality for other modules. This is done by adding Integration Events to our code.

Where the Subscriber that needs to respond to this Publisher is in another module we need to extend the functionality using JSON interfaces.

First, we create a Codeunit within the Publisher module with Subscribers. The parameters in the Subscribers are converted to JSON and passed to the possible subscriber modules using the “ExecuteMethodInApps” function above.

The module that is extending this functionality will be able to answer to these request and supply the required response.

Azure Function

The last example we will show is the Azure Function. Some functionality requires execution in an Azure Function.

By making sure that our Azure Function understands the same JSON format used in our JSON Interface Codeunit we can easily prepare the request and read the response using the same methods.

We have the Azure Function Execution in that same JSON Codeunit. Hence, easily prepare the request and call the function in a similar way as for other interfaces.

The request JSON is posted to the Azure Function and the result read with a single function.

We use the “OnBeforeExecuteAzureFunction” event with a manual binding for our Unit Tests.

In the Azure Function we read the request with standard JSON functions

Then based on the Method we call each functionality with the request and write the response to the response JSON.

Conclusion

Having standard ways of talking between modules and solutions has opened up for a lot of flexibility. We like to keep our solutions as small as possible.

We could mix “Methods” and “Versions” if we at later time need to be able to extend some of the interfaces. We need to honor the contract we have made for the interfaces. We must not make breaking changes to the interfaces, but we sure can extend them without any problems.

By attaching the JSON Interface Codeunit to the post I hope that you will use this pattern in your solutions. Use the Code freely. It is supplies as-is and without any responsibility, obligations or requirements.

JSON Interface – prerequisites

There are two objects we use in all JSON interfaces. We use the TempBlob table and our custom JSON Interface Codeunit.

Abstract

JSON interface uses the same concept as a web service. The endpoint is defined by the Codeunit Name and the caller always supplies a form of request data (JSON) and expects a response data (JSON).

These interface calls therefore are only internal to the Business Central (NAV) server and are very fast. All the data is handled in memory only.

We define these interfaces by Endpoints. Some Endpoints have Methods. We call these Endpoints with a JSON. The JSON structure is predefined and every interface respects the same structure.

We have a single Codeunit that knows how to handle this JSON structure. Passing JSON to an interface requires a data container.

Interface Data

TempBlob is table 99008535. The table is simple but is has a lot of useful procedures.

Wikipedia says: A Binary Large OBject (BLOB) is a collection of binary data stored as a single entity in a database management system. Blobs are typically imagesaudio or other multimedia objects, though sometimes binary executable code is stored as a blob. Database support for blobs is not universal.

We use this BLOB for our JSON data when we send a request to an interface and the interface response is also JSON in that same BLOB field.

For people that have been working with web requests we can say that TempBlob.Blob is used both for RequestStream and for ResponseStream.

TempBlob is only used as a form of Stream. We never use TempBlob to store data. We never do TempBlob.Get() or TempBlob.Insert(). And, even if the name indicates that this is a temporary record, we don’t define the TempBlob Record variable as temporary. There is no need for that since we never do any database call for this record.

Interface Helper Codeunit

We use a single Codeunit in all our solutions to prepare both request and response JSON and also to read from the request on the other end.

We have created a Codeunit that includes all the required procedures for the interface communication.

We have three functions to handle the basics;

  • procedure Initialize()
  • procedure InitializeFromTempBlob(TempBlob: Record TempBlob)
  • procedure GetAsTempBlob(var TempBlob: Record TempBlob)

A typical flow of executions is to start by initializing the JSON. Then we add data to that JSON. Before we execute the interface Codeunit we use GetAsTempBlob to write the JSON into TempBlob.Blob. Every Interface Codeunit expects a TempBlob record to be passed to the OnRun() trigger.

Inside the Interface Codeunit we initialize the JSON from the passed TempBlob record. At this stage we have access to all the data that was added to the JSON on the request side.

And, since the interface Codeunit will return TempBlob as well, we must make sure to put the response JSON in there before the execution ends.

JSON structure

The JSON is an array that contains one or more objects. An JSON array is represented with square brackets.

The first object in the JSON array is the variable storage. This is an example of a JSON that passes two variables to the interface Codeunit.

All variables are stored in the XML format, using FORMAT(<variable>,0,9) and evaluated back using EVALUATE(<variable>,<json text value>,9). The JSON can then have multiple record related objects after the variable storage.

Adding data to the JSON

We have the following procedures for adding data to the JSON;

  • procedure AddRecordID(Variant: Variant)
  • procedure AddTempTable(TableName: Text; Variant: Variant)
  • procedure AddFilteredTable(TableName: Text; FieldNameFilter: Text; Variant: Variant)
  • procedure AddRecordFields(Variant: Variant)
  • procedure AddVariable(VariableName: Text; Value: Variant)
  • procedure AddEncryptedVariable(VariableName: Text; Value: Text)

I will write a more detailed blog about each of these methods and give examples of how we use them, but for now I will just do a short explanation of their usage.

If we need to pass a reference to a database table we pass the Record ID. Inside the interface Codeunit we can get the database record based on that record. Each Record ID that we add to the JSON is stored with the Table Name and we use either of these two procedures to retrieve the record.

  • procedure GetRecord(var RecRef: RecordRef): Boolean
  • procedure GetRecordByTableName(TableName: Text; var RecRef: RecordRef): Boolean

If we need to pass more than one record we can use pass all records inside the current filter and retrieve the result with

  • procedure UpdateFilteredTable(TableName: Text; KeyFieldName: Text; var RecRef: RecordRef): Boolean

A fully populated temporary table with table view and table filters can be passed to the interface Codeunit by adding it to the JSON by name. When we use

  • procedure GetTempTable(TableName: Text; var RecRef: RecordRef): Boolean

in the interface Codeunit to retrieve the temporary table we will get the whole table, not just the filtered content.

We sometimes need to give interface Codeunits access to the record that we are creating. Similar to the OnBeforeInsert() system event. If we add the record fields to the JSON we can use

  • procedure GetRecordFields(var RecRef: RecordRef): Boolean

on the other end to retrieve the record and add or alter any field content before returning it back to the caller.

We have several procedures available to retrieve the variable values that we pass to the interface Codeunit.

  • procedure GetVariableValue(var Value: Variant; VariableName: Text): Boolean
  • procedure GetVariableTextValue(var TextValue: Text; VariableName: Text): Boolean
  • procedure GetVariableBooleanValue(var BooleanValue: Boolean; VariableName: Text): Boolean
  • procedure GetVariableDateValue(var DateValue: Date; VariableName: Text): Boolean
  • procedure GetVariableDateTimeValue(var DateTimeValue: DateTime; VariableName: Text): Boolean
  • procedure GetVariableDecimalValue(var DecimalValue: Decimal; VariableName: Text): Boolean
  • procedure GetVariableIntegerValue(var IntegerValue: Integer; VariableName: Text): Boolean
  • procedure GetVariableGUIDValue(var GuidValue: Guid; VariableName: Text): Boolean
  • procedure GetVariableBLOBValue(var TempBlob: Record TempBlob; VariableName: Text): Boolean
  • procedure GetVariableBLOBValueBase64String(var TempBlob: Record TempBlob; VariableName: Text): Boolean
  • procedure GetEncryptedVariableTextValue(var TextValue: Text; VariableName: Text): Boolean

We use Base 64 methods in the JSON. By passing the BLOB to TempBlob.Blob we can use

and then

on the other end to pass a binary content, like images or PDFs.

Finally, we have the possibility to add and encrypt values that we place in the JSON. On the other end we can then decrypt the data to be used. This we use extensively when we pass sensitive data to and from our Azure Function.

Calling an interface Codeunit

As promised I will write more detailed blogs with examples. This is the current list of procedures we use to call interfaces;

  • procedure ExecuteInterfaceCodeunitIfExists(CodeunitName: Text; var TempBlob: Record TempBlob; ErrorIfNotFound: Text)
  • procedure TryExecuteInterfaceCodeunitIfExists(CodeunitName: Text; var TempBlob: Record TempBlob; ErrorIfNotFound: Text): Boolean
  • procedure TryExecuteCodeunitIfExists(CodeunitName: Text; ErrorIfNotFound: Text) Success: Boolean
  • procedure ExecuteAzureFunction() Success: Boolean

The first two expect a JSON to be passed using TempBlob. The third one we use to check for a simple true/false. We have no request data but we read the ‘Success’ variable from the response JSON.

For some of our functionality we use an Azure Function. We have created our function to read the same JSON structure we use internally. We also expect our Azure Function to respond with the sames JSON structure. By doing it that way, we can use the same functions to prepare the request and to read from the response as we do for our internal interfaces.