Cross-Model Rules & Workspace Membership Use relational context to enforce assignee membership invariants
Phase 14 - Service & Business Logic Architecture Volume 04 - Professional Backend
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Phase 14 turns CRUD-oriented service methods into explicit application rules and workflows while keeping infrastructure simple.
Cross-model business rules require context An assigneeId is not valid merely because the User exists. The Task Project determines a Workspace, and the User must have a Membership in that Workspace.
const project = await prisma.project.findUnique({ where: { id: input.projectId }, select: { id: true, workspaceId: true }, });
const membership = await prisma.membership.findUnique({ where: { workspaceId_userId: { workspaceId: project.workspaceId, userId: input.assigneeId, }, }, });
The composite unique key becomes useful Phase 10 intentionally defined @@unique([workspaceId, userId]). That schema design now gives the service an unambiguous and efficient way to ask whether this exact membership exists.
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workspaceId
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candidate assigneeId
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The service composes relational facts into an application rule.
A 409 is more useful than a database crash ASSIGNEE_NOT_WORKSPACE_MEMBER is a deliberate business conflict: the request is syntactically valid, the User may exist, but the requested state conflicts with TaskFlow workspace rules.
This check does not ask whether the current caller is allowed to assign the Task. That is authorization and arrives later. Phase 14 only proves the target assignee satisfies the Task domain invariant.
Cross Model Rules and Workspace Membership matters because it changes a real boundary in TaskFlow. The goal is to understand the inputs, owner, observable output, and failure modes before adding more abstraction.
Restate the goal of “Cross Model Rules and Workspace Membership” as one observable behavior. Write the success signal before touching code.
Trace the boundary map: repository root → workspace package → dependency graph → task runner → artifact. Mark the one boundary this lesson changes.
Inspect the current repository state and record the exact files, route, table, or runtime involved. Avoid creating an abstraction before you can name the existing owner.
Implement the smallest vertical slice. Add one coherent change, run the narrowest verification command, and read the output before continuing.
Connect the slice to TaskFlow’s phase artifact: Refactored task service with explicit policies/invariants and thin controllers.. Verify behavior from the outside as a user or API client would.
Create one controlled failure that is safe to reproduce. Predict the symptom first, capture evidence, locate the earliest broken boundary, then fix only that cause.
Close the reference and rebuild or explain the core change from memory. Record what you would monitor or test before trusting the same change in production.
model WorkspaceMember {
workspaceId String
userId String
role WorkspaceRole
workspace Workspace @relation(fields: [workspaceId], references: [id])
user User @relation(fields: [userId], references: [id])
@@id([workspaceId, userId])
}Do not copy this as a finished answer. Predict what each boundary does, type the smallest useful slice, run it, then compare the result with your prediction.
Return to the nearest observable boundary: input, network, process log, database, or rendered UI. Compare actual evidence with the predicted path.
Change one variable at a time and reproduce the original failure after the fix; otherwise you have correlation, not diagnosis.
Without copying the final source, create a second small scenario that applies “Cross Model Rules and Workspace Membership” to a different TaskFlow resource or input. Write the acceptance criteria first, implement it, and provide the evidence that each criterion is satisfied.
Add a use-case method whose inputs/outputs make orchestration visible.
Use the smallest change that demonstrates this lesson. Stop after it works and capture evidence.Methods named only after CRUD verbs when workflow intent matters
Predict the symptom before causing the failure. Then locate the earliest boundary where reality diverges from expectation.Why does this responsibility live here, what input does it trust, what output proves success, and what would go wrong if another layer owned it?
If your explanation is vague, repeat the boundary trace before moving on.Close the reference. Reproduce the core idea from memory or explain the exact request/data flow aloud. Then check your diff or notes for accidental shortcuts that bypass validation, authorization, error handling, or verification earned in earlier phases.