[@loopback/sequelize] BelongsTo relation sets target entity column name on the source entity

[KalleV]

Describe the bug

I encountered an issue with a @BelongsTo relation adding column names to a SELECT query that did not exist on the source table when testing the sequelize extension. I traced it to this section:

loopback-next/extensions/sequelize/src/sequelize/sequelize.repository.base.ts

Lines 626 to 634 in f751040

	const foreignKey = (
	entityClass.definition.relations[key] as BelongsToDefinition
	).keyTo;
	sourceModel.belongsTo(targetModel, {
	foreignKey: {name: foreignKey},
	// Which client will pass on in loopback style include filter, eg. `include: ["thisName"]`
	as: entityClass.definition.relations[key].name,
	});

The "keyTo" assignment to the "foreignKey" causes the target entity column to be assigned back to the source entity by Sequelize leading to a broken query: https://github.com/sequelize/sequelize/blob/a9fd5010809366eb50fa9d6fc4bf0612a9d1d751/src/associations/mixin.js#L38. Looks like the fix is to swap the "keyTo" to "keyFrom" because the Sequelize belongsTo "foreignKey" is the source entity column name rather than the target.

- const foreignKey = (
-          entityClass.definition.relations[key] as BelongsToDefinition
-        ).keyTo;
+ const relation = entityClass.definition.relations[key] as BelongsToDefinition;
+ const foreignKey = relation.keyFrom;
+ const targetKey = relation.keyTo;
sourceModel.belongsTo(targetModel, {
  foreignKey: {name: foreignKey},
+ targetKey,

  // Which client will pass on in loopback style include filter, eg. `include: ["thisName"]`
  as: entityClass.definition.relations[key].name,
});

References:
https://sequelize.org/api/v6/class/src/model.js~model#static-method-belongsTo
https://loopback.io/doc/en/lb4/BelongsTo-relation.html#relation-metadata

Logs

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Additional information

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Reproduction

N/A

[shubhamp-sf]

The insights you shared make sense to me but can you share details on how to reproduce it?
As of now the tests are present for belongsTo with the definition something like this: todo.model.ts#L25 is working.

[KalleV]

It seems like the reproduction steps on #9617 apply to this one too.