Скачать или смотреть How to Keep the Many Side Unique in a One-to-Many Relationship Using TypeORM

Discover how to ensure the uniqueness of the `many` side in a one-to-many relationship using TypeORM in your database, perfect for handling cryptocurrency daily data without duplicates.
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Ensuring Uniqueness in a One-to-Many Relationship with TypeORM

When working with databases, particularly in scenarios where you're dealing with the same entity multiple times (like scraping cryptocurrency data), it's important to handle duplication effectively. If you're using TypeORM in a Node.js application to manage a one-to-many relationship, you might find yourself facing the issue of duplicate data entries.

In this guide, we will explore a solution to maintain the uniqueness of entries in the 'many' side of a one-to-many relationship by using TypeORM, specifically in relation to cryptocurrency data where we might encounter the same symbol multiple times.

The Problem: Duplicate Entries in Daily Data

Consider the following scenario: You're building a program that scrapes an API for cryptocurrency symbols and their daily price history. When a symbol, say "BTC" for Bitcoin is scraped multiple times, your program might inadvertently insert duplicate records into the database. This happens because the design of your database tables does not prevent this duplication, leading to inefficiencies and inflated storage.

Understanding Your Tables

To clarify the issue, let’s look at the structure of the two tables involved:

CryptoSymbol Table - Holds details about the cryptocurrency symbols.

CryptoDailyData Table - Keeps track of daily price history for each cryptocurrency symbol.

Here is a simplified representation of the TypeORM entities:

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

Due to this structure, each time the program encounters the same symbol, it creates a new entry in the CryptoDailyData table, including duplicate daily data.

The Solution: Implementing Composite Unique Keys

To effectively manage this issue, we can leverage composite unique keys. This means that we can ensure that the combination of the cryptocurrency symbol and the date is unique in the CryptoDailyData table.

Steps to Create a Composite Unique Key

Here is a step-by-step breakdown of how to implement this solution:

Change the Type of the Date Column:
Instead of using a datetime type, you will switch to using the date type.

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

Define the Foreign Key:
Specify the join column for the @ ManyToOne relationship. This allows you to create a clear reference to the CryptoSymbol entity.

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

Create the Composite Unique Key:
Add the composite unique key to the CryptoDailyData entity to ensure that each combination of crypto_symbol_id and date is unique.

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

With these changes, if your program tries to insert data for the same cryptocurrency symbol on the same date, it will throw an error, effectively preventing duplicate entries.

Final Entity Structure

After implementing the above changes, your CryptoDailyData entity would look like this:

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

Additional Layer of Protection

While implementing a composite unique key at the database level is essential, it's also advisable to perform a check at the application level. Before attempting to insert a new record, always determine whether a record for a specific cryptocurrency on a given day already exists. This additional safeguard can help streamline your processes and prevent unnecessary database operations.

Conclusion

By following these steps to create a composite unique key, you can ensure that the "many" sides of your one-to-many relationships remain unique in your TypeORM model. This approach is crucial for applications that frequently deal with repeated data, such as those scra