TypeScript Upsert PostgreSQL Sequence Error: "Relation 'customers_sq' Does Not Exist"

Understanding PostgreSQL Sequence Errors in Upserts

Working with PostgreSQL and TypeScript, especially during an upsert operation, can sometimes lead to unexpected sequence errors. One such common error involves the database not recognizing a sequence, leading to messages like "relation 'customers_sq' does not exist". This error typically occurs when referencing sequences incorrectly within SQL queries.

In this article, we will explore a real-world scenario where a developer encounters this issue while performing an upsert. We will discuss how sequences work in PostgreSQL and identify common mistakes when referencing them, particularly in TypeScript.

Often, these errors arise due to incorrect syntax or schema scoping, especially when dealing with sequences in different database schemas or namespaces. Debugging the issue requires careful attention to how PostgreSQL expects sequences to be referenced in queries.

By the end of this guide, you will have a clearer understanding of why this "relation does not exist" error happens and the steps you can take to fix it. This includes practical tips for resolving sequence reference problems and ensuring your upserts work as intended in PostgreSQL.

Command	Example of Use
NEXTVAL('sequence_name')	This PostgreSQL function retrieves the next value from a specified sequence. It is critical in generating unique IDs for rows during insertions. Example: NEXTVAL('db.customers_sq') fetches the next value from the sequence in the "db" schema.
ON CONFLICT ("column") DO UPDATE	Used in PostgreSQL upsert operations, this command handles cases where an insertion would result in a conflict on a unique column. Instead of failing, it updates the conflicting row. Example: ON CONFLICT ("id") DO UPDATE SET "name" = $1.
pg_sequences	A PostgreSQL catalog view that provides information about all sequences in the database. This is used to query metadata about sequences, such as their existence in a specific schema. Example: SELECT * FROM pg_sequences WHERE sequencename = 'customers_sq';
pool.query()	A method from the PostgreSQL node module , used to execute SQL queries. It handles database connections efficiently, pooling them for reuse. Example: pool.query(SAVE_CUSTOMER, [name]) executes the insert/update SQL for a customer.
mockResolvedValueOnce()	A Jest method used in testing. It mocks the response of a function to return a specific value once. In this case, it simulates the successful execution of a database query. Example: pool.query.mockResolvedValueOnce({}).
mockRejectedValueOnce()	This Jest function mocks an error being thrown by a promise, simulating a failed query. Example: pool.query.mockRejectedValueOnce(new Error('Sequence not found')) replicates an error where a sequence is missing.
expect.toThrow()	A Jest assertion that verifies if a function throws a specified error. This is essential for testing how the function behaves when an error occurs. Example: expect(saveCustomer('John')).rejects.toThrow('Sequence not found');.
schemaname	A column in that indicates the schema where the sequence is defined. It helps differentiate between sequences with the same name but in different schemas. Example: SELECT * FROM pg_sequences WHERE schemaname = 'db';.

How to Handle PostgreSQL Sequence Errors in Upserts

The scripts provided in the earlier examples are designed to address a common issue that arises when referencing sequences in PostgreSQL, especially during an operation in TypeScript. An upsert operation either inserts new records or updates existing ones, making the correct use of sequences vital for maintaining unique primary keys. The key issue here stems from incorrect sequence referencing, which leads to the error: "relation '

The first script resolves this issue by ensuring that the sequence is correctly referenced with schema awareness. When we use , we specify both the schema ("db") and the sequence ("customers_sq"), ensuring that PostgreSQL looks for the sequence in the correct context. If the schema is omitted or improperly referenced, PostgreSQL may not find the sequence, triggering the error. This command works within a in TypeScript, ensuring that user input is securely passed into the query to prevent SQL injection attacks.

Additionally, an alternative solution is provided using dynamic sequence checking. This approach queries the PostgreSQL catalog view, , to verify the existence of the sequence before attempting to insert or update the record. This not only adds a layer of error handling but also ensures that the script is flexible and robust, able to adapt to changes in the database schema. By checking for the sequence dynamically, the system can provide a more informative error message if the sequence is missing or incorrectly referenced, improving the debugging process.

Lastly, unit testing is an essential part of the solution. The test suite is used to ensure that the upsert function behaves as expected. In the tests, both successful operations and error cases, such as missing sequences, are handled. The test cases use methods like and to simulate how the database responds to queries. By verifying that the correct SQL commands are executed and that errors are appropriately thrown when sequences are missing, the test cases help ensure the reliability of the solution across different environments.

// TypeScript - Upsert solution using parameterized query with correct sequence reference
import { Pool } from 'pg';
const pool = new Pool();
const SAVE_CUSTOMER = `
  INSERT INTO "db"."customers" ("id", "name")
  VALUES (NEXTVAL('db.customers_sq'), $1)
  ON CONFLICT ("id") DO UPDATE SET "name" = $1`;
async function saveCustomer(name: string) {
  try {
    await pool.query(SAVE_CUSTOMER, [name]);
    console.log('Customer saved successfully');
  } catch (error) {
    console.error('Error saving customer:', error.message);
  }
}

// TypeScript - Dynamic sequence referencing with schema awareness
import { Pool } from 'pg';
const pool = new Pool();
async function saveCustomer(name: string) {
  try {
    const checkSequence = `SELECT EXISTS (
      SELECT 1 FROM pg_sequences WHERE schemaname = 'db' AND sequencename = 'customers_sq');`;
    const sequenceExists = await pool.query(checkSequence);
    if (!sequenceExists.rows[0].exists) {
      throw new Error('Sequence not found');
    }
    const SAVE_CUSTOMER = `
      INSERT INTO "db"."customers" ("id", "name")
      VALUES (NEXTVAL('db.customers_sq'), $1)
      ON CONFLICT ("id") DO UPDATE SET "name" = $1`;
    await pool.query(SAVE_CUSTOMER, [name]);
    console.log('Customer saved successfully');
  } catch (error) {
    console.error('Error saving customer:', error.message);
  }
}

// Jest - Unit test for saveCustomer function
import { saveCustomer } from './saveCustomer';
import { pool } from 'pg';
jest.mock('pg');
describe('saveCustomer', () => {
  it('should insert new customer if no conflict', async () => {
    pool.query.mockResolvedValueOnce({});
    await saveCustomer('John Doe');
    expect(pool.query).toHaveBeenCalledWith(expect.any(String), ['John Doe']);
  });
  it('should throw error if sequence does not exist', async () => {
    pool.query.mockRejectedValueOnce(new Error('Sequence not found'));
    await expect(saveCustomer('John Doe')).rejects.toThrow('Sequence not found');
  });
});

Key Factors Behind PostgreSQL Sequence Errors

One aspect not previously covered is how PostgreSQL handles when it comes to database objects like sequences. PostgreSQL defaults to treating unquoted identifiers as lowercase. This means that if a sequence name was created with uppercase letters but referenced without quotes, PostgreSQL will automatically search for the lowercase version. For instance, if the sequence was created as "Customers_SQ" but referenced as , it may lead to the error, "relation does not exist". Using double quotes around the sequence name, such as , ensures PostgreSQL uses the exact case as defined.

Another crucial aspect is schema visibility in PostgreSQL. By default, PostgreSQL searches for sequences in the schema that’s first in the search path unless a schema is explicitly defined. If the sequence resides in a different schema, referencing it without specifying the schema (e.g., ) can lead to a sequence-not-found error. Developers need to either adjust the search path or reference the schema explicitly to avoid this problem, especially in complex database structures with multiple schemas.

Lastly, it’s important to mention database . If a user does not have the necessary privileges to access or modify a sequence, they may encounter errors like "relation does not exist". Granting the correct permissions to roles interacting with the database sequence ensures they can retrieve the next value via without issues. This is especially important in production environments with strict access controls and multiple roles interacting with the database.

1. What does the error "relation does not exist" mean in PostgreSQL?
2. This error typically means that PostgreSQL cannot find the sequence or table you’re referencing, often due to incorrect sequence naming, schema visibility, or case sensitivity.
3. How can I fix case sensitivity issues in PostgreSQL sequence references?
4. Use double quotes around the sequence name like to ensure PostgreSQL uses the correct case as defined during creation.
5. What is the role of schemas in sequence errors?
6. If a sequence is not in the default schema, you must explicitly reference the schema in your command, such as .
7. How do I check if a sequence exists in PostgreSQL?
8. You can query the table to verify the existence of a sequence. Example:
9. What should I do if I lack permissions to access a sequence?
10. Make sure the user role has the appropriate privileges. You can grant access using the command .

To resolve the error, "relation 'customers_sq' does not exist", ensure the correct schema is referenced, and the sequence name matches PostgreSQL’s case sensitivity rules. Double-check sequence permissions to avoid access issues during upsert operations.

Always use carefully and verify that the sequence exists in your PostgreSQL database by querying the catalog. Following these debugging steps ensures that your database operations run smoothly and efficiently without sequence-related errors.