Скачать или смотреть How to Update Parameterized SELECT Query in Node.js with Postgres

Learn how to dynamically update parameterized SELECT queries in Node.js using Postgres. Here’s a step-by-step guide to fetch specific columns from your database effectively.
---
This video is based on the question https://stackoverflow.com/q/72916465/ asked by the user 'Ged0jzn4' ( https://stackoverflow.com/u/17451659/ ) and on the answer https://stackoverflow.com/a/72916869/ provided by the user 'Bergi' ( https://stackoverflow.com/u/1048572/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: How to update parameterized SELECT query in node.js with postgres

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Update Parameterized SELECT Query in Node.js with Postgres

When working with databases, especially in a Node.js environment with PostgreSQL, developers often encounter challenges when trying to fetch specific data using parameterized queries. One common scenario is retrieving a user's balance in a specific currency, but instead of getting the expected results, you may end up with undesired outputs. In this guide, we will tackle this issue and provide a detailed solution on how to correctly fetch specific columns from your database.

The Problem: Fetching Specific Columns

Consider a database table structured as follows:

user_idUSDEURGBP1231231.22.33.4You want to retrieve the balance for a specific user and currency, such as user_id 123123 and currency 'USD'. However, when you run your SQL query, instead of getting the desired format like {'USD': 1.2}, you might get an array like [ {'?column?': 'USD'} ]. This issue arises because you can't parameterize column names in a SQL query directly.

The Solution: Dynamic SQL String Construction

To correctly fetch the specified column for a user, you will need to construct your SQL query dynamically. Below, we’ll break down the steps needed to resolve this issue.

Step 1: Set Up the Database Connection

First, ensure that you have the necessary PostgreSQL connection configuration set up in your Node.js application by importing your environment variables.

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Modify the Query Execution Method

We'll create an async function to fetch the balance, ensuring we build the SQL string dynamically. Here's how you can implement this:

[[See Video to Reveal this Text or Code Snippet]]

In this code:

We use client.escapeIdentifier(currency) to safely include the currency column name in the SQL string.

The user_id is passed as a parameter to prevent SQL injection attacks.

Step 3: Validate Currency Input

It’s also important to validate that the currency provided is indeed a valid column name within your database. You can do this with a simple conditional check:

[[See Video to Reveal this Text or Code Snippet]]

This validation step ensures that the user cannot input an arbitrary string that could lead to potential errors or security issues.

Conclusion

With the steps outlined above, you should now be able to effectively fetch specific balances for a user based on the currency requested. By constructing your SQL query dynamically and validating inputs, you can mitigate risks and ensure that your application behaves as expected.

If you follow these best practices, working with databases in Node.js and PostgreSQL can become a seamless and efficient process. Happy coding!