domain-modeling-made-functional-in-kotlin

Examples from Domain Modeling Made Functional Tackle Software Complexity with Domain-Driven Design and F# book translated to Kotlin

Idea

I was looking for production like examples of code based on Functional Programming paradigm. I found the aforementioned book which focuses on using Functional Programming with Domain Driven Design. The book contains extensive code samples So I found even more than I was looking for ;-).

I try to apply FP but in Kotlin. So I thought that it could be interesting to convert the code from book to Kotlin.

Changes

It is not 1 to 1 copy. I have changed the original in several areas:

implementation is based on Arrow - functional library for Kotlin
application assembly and REST endpoint is based on Spring Boot
data validation is based on arrow types
base type for simple types to support comparison and string representation -> replaced with value classes where possible
dropped String50 type
dependencies - only immediate dependencies are provided instead of dependencies of dependencies
orderId and orderLineId are alphanumeric with capital letters only

Original Code

The code in /src/original directory was copied from sources attached to the book.

Testing

Start the Application

To start the application execute following command:

./gradlew bootRun

Place Valid Order

Execute the following command in shell:

curl --location --request POST 'http://localhost:8080/orders' \
--header 'Content-Type: application/json' \
--data-raw '{
    "orderId": "ORD1",
    "customerInfo": {
        "firstName": "Jan",
        "lastName": "Kowalski",
        "emailAddress": "jan@kowalski.com"
    },
    "shippingAddress": {
        "addressLine1": "Some Street 1",
        "city": "Los Angeles",
        "zipCode": "12345"
    },
    "billingAddress": {
        "addressLine1": "Other Street 4",
        "addressLine2": "Appatment 42",
        "city": "Beverly Hills",
        "zipCode": "90210"
    },
    "lines": [
        {
            "orderLineId": "LN1"
            "productCode": "W1234",
            "quantity": 10
        },
        {
            "orderLineId": "LN2",
            "productCode": "G123",
            "quantity": 0.75
        }
    ]
}
'

Place Invalid Order

Execution of following command

curl --location --request POST 'http://localhost:8080/orders' \
--header 'Content-Type: application/json' \
--data-raw '{
    "orderId": "1345",
    "customerInfo": {
        "firstName": "Jan",
        "lastName": "Kowalski",
        "emailAddress": "jan@kowalski.com"
    },
    "shippingAddress": {
        "addressLine1": "Some Street 1",
        "city": "Los Angeles",
        "zipCode": "12345"
    },
    "billingAddress": {
        "addressLine1": "",
        "addressLine2": "Appatment 42",
        "city": "Beverly Hills",
        "zipCode": "90210a"
    },
    "lines": [
        {
            "orderLineId": "LN1",
            "productCode": "W1234",
            "quantity": 101111
        },
        {
            "orderLineId": "LN2",
            "productCode": "G123",
            "quantity": 0.001
        }
    ]
}
'

Should return validation errors:

{
    "code": "ValidationError",
    "message": "Validation errors",
    "validationErrors": [
        {
            "path": "billingAddress/addressLine1",
            "message": "The length of <> should be between <1> and <50>"
        },
        {
            "path": "billingAddress/zipCode",
            "message": "'90210a' must match the pattern '\\d{5}'"
        },
        {
            "path": "lines[0]/quantity",
            "message": "The <101111> should be between <1> and <1000>"
        },
        {
            "path": "lines[1]/quantity",
            "message": "The <0.001> should be between <0.05> and <100.00>"
        }
    ]
}

TODO

Implement Address Validation

The validation incorporates address check which is an asynchronous operation. Because of that it enforces that address and order validation become also synchronous. Async/suspend does not blend well with Validated. Need to find a smart way to solve the problem.

dnowak/domain-modeling-made-functional-in-kotlin