cursor-plugin-convex-rule-no-date-now-in-queries

name	cursor-plugin-convex-rule-no-date-now-in-queries
description	Never use Date.now() in queries as it breaks caching and reactivity
metadata	{"version":"0.1.0"}

Avoid Date.now() in Queries

Never use Date.now() or new Date() inside query functions. It prevents proper caching and breaks reactive subscriptions.

Why

Queries should be deterministic. Using Date.now() means the query returns different results every millisecond, defeating Convex's reactivity system.

Bad Pattern

export const getActiveTasks = query({
  handler: async (ctx) => {
    const now = Date.now(); // ❌ Don't do this
    return await ctx.db
      .query("tasks")
      .filter(q => q.lt(q.field("dueDate"), now))
      .collect();
  },
});

Good Solutions

Option 1: Pass Time as Argument

export const getActiveTasks = query({
  args: { now: v.number() },
  handler: async (ctx, args) => {
    return await ctx.db
      .query("tasks")
      .filter(q => q.lt(q.field("dueDate"), args.now))
      .collect();
  },
});

// Client passes current time
const tasks = useQuery(api.tasks.getActiveTasks, { now: Date.now() });

Option 2: Use Status Fields with Scheduled Functions

// Update status periodically with a cron job
export const updateTaskStatuses = internalMutation({
  handler: async (ctx) => {
    const now = Date.now();
    const expiredTasks = await ctx.db
      .query("tasks")
      .withIndex("by_status", q => q.eq("status", "active"))
      .filter(q => q.lt(q.field("dueDate"), now))
      .collect();

    for (const task of expiredTasks) {
      await ctx.db.patch(task._id, { status: "expired" });
    }
  },
});

// Query is simple and efficient
export const getActiveTasks = query({
  handler: async (ctx) => {
    return await ctx.db
      .query("tasks")
      .withIndex("by_status",  => q.(, ))
      .();
  },
});

Option 3: Use Coarser Time Granularity

If you need day-level filtering:

export const getToday = query({
  args: { today: v.string() }, // "2024-01-15"
  handler: async (ctx, args) => {
    return await ctx.db
      .query("events")
      .withIndex("by_date", q => q.eq("date", args.today))
      .collect();
  },
});