Write Once, Validate Everywhere: Optimizing DynamoDB Interaction with Higher-Order Functions

In the process of building robust applications that interact with databases like AWS DynamoDB, we often find ourselves writing service layers that perform various CRUD operations. A common necessity in such layers is to ensure that the methods handling these operations receive all the required parameters before proceeding with database interactions. This often leads to repetitive blocks of parameter validation code scattered across multiple service methods, cluttering the codebase with boilerplate checks and throwing errors when parameters are missing. This not only makes the code less maintainable but also hinders scalability as every new method potentially duplicates these checks, increasing the risk of inconsistencies and bugs.

For example, consider a DynamoService class with multiple methods interacting with DynamoDB. Each method starts by verifying if the necessary parameters are provided, and if not, it logs an error and throws an exception. This repetition violates the DRY (Don't Repeat Yourself) principle, making the code verbose and harder to manage. If we look at the dynamodbScanHelper method below, the parameter validation for TableName is a pattern that would repeat across similar methods such as dynamodbQueryHelper or dynamodbPutItemHelper, each time checking for their respective required parameters.

class DynamoService {
    constructor(docClient) {
        this.docClient = docClient;
    }

    async dynamodbPutHelper({ TableName, Item }) {
        // Parameter validation for TableName
        if (!TableName || !Item) {
            logger.error("TableName & Item are required", {
                data: { TableName }
            });
            throw new Error("TableName & Item are required");
        }

        // If validation passes, proceed with the scan operation
        try {
            // DynamoDB put logic...
        } catch (error) {
            logger.error("Error performing DynamoDB put", { data: error });
            throw error;
        }
    }

    // Other service methods...
}

High-Order Functions for Abstraction

you can abstract the repetitive parameter validation logic by creating a higher-order function (HOF) or a validation function that you can call within each method of your DynamoService. This approach centralizes the validation logic, making your code DRY (Don't Repeat Yourself) and easier to manage.

Here’s an example of how you can create a validation function and use it within your service methods:

Step 1: Create a Validation Function

Create a general-purpose validation function that checks for the presence of required parameters:

function validateParams(params, requiredParams) {
    for (const param of requiredParams) {
        if (!params[param]) {
            logger.error(`${param} is required`, { data: params });
            throw new Error(`${param} is required`);
        }
    }
}

Step 2: Use the Validation Function in Your Service Methods

Now, in your DynamoService methods, call the validateParams function, passing the parameters and an array of required parameter names:

async dynamodbScanHelper({TableName}) {
    validateParams({ TableName }, ['TableName']);
    
    // Proceed with the function if validation passes
}

Step 3: Create a Higher-Order Function for Validation

If you want to take it a step further and not even have to call the validateParams in every function, you can create a HOF that does the validation before executing the function:

function withValidation(fn, requiredParams) {
    return async function(params) {
        validateParams(params, requiredParams);
        return await fn.call(this, params);
    };
}

// Example usage
class DynamoService {
    // Bind the method to 'this' to maintain context
    dynamodbPutHelper = withValidation(async function({TableName, Item}) {
        // Function logic here after validation has passed
    }, ['TableName', 'Item']);
}

Using withValidation, you wrap your actual service method with a validation step that occurs before the method's logic is executed. This way, you can define the validation rules for each method once and have them applied automatically.

These patterns will help you avoid repetitive validation checks across different functions in your DynamoService, making the code more concise and easier to maintain.

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