Sequelize Associations: How a Misplaced belongsTo Broke Our Query (and How to Fix It)
Originally published on shorterloop.com.

As developers, we’ve all faced that moment of dread: your code should work, but instead, your logs fill with cryptic SQL errors. Recently, a team ran into a baffling Sequelize issue — a simple update query for a feedback system suddenly demanded a non-existent feedback_item_id
field. Let’s dissect what went wrong, why, and how to avoid this trap.
module.exports = function (sequelize, DataTypes) {
const feedbackItem = sequelize.define("idm_feedback_items", {
// ... title, status, etc. ...
status: {
type: DataTypes.STRING,
defaultValue: STATUS.active
},
user_id: DataTypes.INTEGER, // Foreign key for user
category_id: DataTypes.INTEGER, // Foreign key for category
});
feedbackItem.associate = (models) => {
// 🚩 Problematic association!
feedbackItem.belongsTo(models.idm_ideas_tags, {
foreignKey: "feedback_item_id",
as: "taggings"
});
// Correct many-to-many setup with tags
feedbackItem.belongsToMany(models.tags, {
through: models.idm_ideas_tags,
foreignKey: "feedback_item_id",
as: "tags"
});
};
return feedbackItem;
};
Everything seemed fine — until they ran an update:
await feedback_items.update(
{ status: "deleted" },
{ where: { external_key: "IDEA-10", product_id: 1131 } }
);
Suddenly, their logs showed:
SELECT ..., `feedback_item_id` FROM `idm_feedback_items` WHERE ...;
The problem? The feedback_item_id
column didn’t exist in their table. Why did Sequelize include it?
The Culprit: Misusing belongsTo
The root cause was an incorrect association. Let’s break it down:
1. The Offending Code
In the associate
function:
feedbackItem.belongsTo(models.idm_ideas_tags, {
foreignKey: "feedback_item_id", // 🚩 Red flag!
as: "taggings"
});
2. Why This Broke
idm_ideas_tags
was a junction table for a many-to-many relationship between feedback items and tags.- Using
belongsTo
incorrectly implied thatidm_feedback_items
had a direct foreign keyfeedback_item_id
pointing to the junction table. - Sequelize assumed
feedback_item_id
was a column inidm_feedback_items
and included it in queries.
The Fix: Use belongsToMany for Junction Tables
Step 1: Remove the Incorrect Association
Delete the problematic belongsTo
block:
// Remove this entirely!
// feedbackItem.belongsTo(models.idm_ideas_tags, { ... });
Step 2: Strengthen the Many-to-Many Setup
Ensure the relationship uses belongsToMany
:
feedbackItem.belongsToMany(models.tags, {
through: models.idm_ideas_tags, // Junction table
foreignKey: "feedback_item_id", // Field in JUNCTION table
otherKey: "tag_id", // Field in JUNCTION table
as: "tags"
});
How This Works:
belongsToMany
tells Sequelize the relationship is managed via a junction table.foreignKey
andotherKey
refer to columns in the junction table, not the main model.
Lessons Learned
1. belongsTo vs. belongsToMany
AssociationUse CaseForeign Key LocationbelongsTo
Many-to-One or One-to-OneCurrent model’s tablebelongsToMany
Many-to-Many (via junction)Junction table
2. Common Pitfalls
- Assuming junction tables need direct associations: They don’t — use
belongsToMany
. - Naming conflicts: Ensure foreign keys in associations don’t clash with existing columns.
3. Debugging Tips
- Log Sequelize queries: Enable
logging: console.log
to spot unexpected fields. - Validate associations: Double-check
foreignKey
andthrough
settings.
Best Practices for Sequelize Associations
- Map Relationships Early: Sketch your schema to identify junction tables and relationship types.
- Use Consistent Naming: Stick to conventions (e.g.,
feedback_item_id
, notfeedbackItemId
). - Test Associations:
it("should load tags via junction table", async () => {
const feedback = await FeedbackItem.findByPk(1, { include: "tags" });
expect(feedback.tags).to.be.an("array");
});
Final Thoughts
Sequelize associations are powerful but require precision. Misusing belongsTo
instead of belongsToMany
is a common pitfall with junction tables. By understanding how these methods map to your schema, you’ll avoid unexpected SQL chaos.
Next time your query includes a mysterious field, check your associations — it might save hours of debugging!
Gotchas to Watch For:
- Accidental
belongsTo
on junction tables. - Typos in foreign key names.
- Forgetting to define both sides of an association.
Further Reading:
Engage: Ever battled unexpected fields in Sequelize? Share your war stories below! 💬
This article was originally published on shorterloop.com.