Junction table not specified for many-to-many relationship b

Error message

Junction table not specified for many-to-many relationship between ${relationship.sourceTable} and ${relationship.targetTable}

What it means

createRelationshipColumns in the builder's relationshipSelectionStore builds columns for imported table relationships. For MANY_TO_MANY relationships it needs a junction (join) table; if relationship.junctionTable is falsy it cannot wire the columns, so it throws this error. It is a configuration-completeness check before any datasource mutation happens.

Source

Thrown at packages/builder/src/components/backend/Datasources/TableImportSelection/relationshipSelectionStore.ts:171

        : undefined
    if (
      relationshipExists(
        sourceTable,
        targetTable,
        relationship,
        junctionTableId
      )
    ) {
      // Relationship already exists, skip creating it
      return false
    }

    if (
      relationship.relationshipType === DatasourceRelationshipType.MANY_TO_MANY
    ) {
      // For many-to-many relationships, we need the junction table
      if (!relationship.junctionTable) {
        throw new Error(
          `Junction table not specified for many-to-many relationship between ${relationship.sourceTable} and ${relationship.targetTable}`
        )
      }

      // Get the junction table entity
      const junctionTable = datasource.entities[relationship.junctionTable]
      if (!junctionTable) {
        throw new Error(
          `Junction table '${relationship.junctionTable}' not found in datasource`
        )
      }

      // Generate unique column names
      const sourceColumnName = generateRelationshipColumnName(
        sourceTable.schema,
        relationship.targetTable,
        relationship.sourceColumn
      )

View on GitHub (pinned to a81a902e9a)

Solutions

Set relationship.junctionTable to the name of the existing join table in datasource.entities before calling createRelationshipColumns.
If the relationship is actually one-to-many, change relationshipType from MANY_TO_MANY so no junction table is required.
Create or import the junction table so it exists in datasource.entities, then retry the import.

Example fix

// before
relationships.push({ sourceTable: "users", targetTable: "roles", relationshipType: DatasourceRelationshipType.MANY_TO_MANY })
// after
relationships.push({ sourceTable: "users", targetTable: "roles", relationshipType: DatasourceRelationshipType.MANY_TO_MANY, junctionTable: "user_roles" })

Defensive patterns

Strategy: validation

Validate before calling

const invalid = relationships.some(r => r.relationshipType === DatasourceRelationshipType.MANY_TO_MANY && !r.junctionTable)
if (invalid) throw new Error("All many-to-many relationships need a junctionTable")

Type guard

const hasJunction = (r: Relationship): r is Relationship & { junctionTable: string } =>
  r.relationshipType !== DatasourceRelationshipType.MANY_TO_MANY || typeof r.junctionTable === "string" && r.junctionTable.length > 0

Try / catch

try {
  await createRelationshipColumns(...)
} catch (e) {
  if (e.message.includes("Junction table not specified")) {
    promptUserForJunctionTable(); return
  }
  throw e
}

Prevention

Always populate junctionTable when building MANY_TO_MANY relationships from schema introspection.
Validate relationship definitions against datasource.entities before calling the import flow.
Let the relationship selection UI derive the junction table instead of constructing payloads manually.

When it happens

Trigger: Calling createRelationshipColumns (via wasCreated) with a relationship whose relationshipType is DatasourceRelationshipType.MANY_TO_MANY and whose junctionTable property is undefined/empty string — e.g. an import payload built outside the relationship selection UI that omitted the junction table.

Common situations: Importing SQL table schemas where join tables were not detected/mapped; hand-crafted or migrated relationship definitions copied from another datasource that lacked junctionTable; UI flows bypassed programmatically so the junction-table picker was never completed.

Related errors

AI-assisted analysis of Budibase/budibase@a81a902e9a (2026-08-29). Data as JSON: /api/errors/f2c9b8c18e764511. Report an issue: GitHub.