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Use assignments to set an initial schedule or lock specific employee-shift pairings that the solver cannot change.

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Use Cases

  • Warm start - Provide an initial solution for faster optimization
  • Fixed assignments - Lock confirmed shifts that cannot change
  • Partial planning - Keep some assignments fixed while optimizing others
  • Incremental scheduling - Add new shifts while preserving existing schedule

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Warm Start

Provide an initial schedule without locking to help the solver find better solutions faster: 
{
  "employees": [
    { "name": "Alice" },
    { "name": "Bob" },
    { "name": "Carol" }
  ],
  "shifts": [
    { "name": "shift-1", "from": "2024-01-01T08:00:00", "to": "2024-01-01T16:00:00", "min": 1, "max": 1 },
    { "name": "shift-2", "from": "2024-01-02T08:00:00", "to": "2024-01-02T16:00:00", "min": 1, "max": 1 }
  ],
  "assignments": [
    { "employee": "Alice", "shift": "shift-1", "locked": false },
    { "employee": "Bob", "shift": "shift-2", "locked": false }
  ]
}
With locked: false, the solver uses these assignments as a starting point but may reassign them if a better solution exists.

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Locked Assignments

Lock assignments that must not change: 
{
  "employees": [
    { "name": "Alice" },
    { "name": "Bob" },
    { "name": "Carol" }
  ],
  "shifts": [
    { "name": "shift-1", "from": "2024-01-01T08:00:00", "to": "2024-01-01T16:00:00", "min": 1, "max": 1 },
    { "name": "shift-2", "from": "2024-01-02T08:00:00", "to": "2024-01-02T16:00:00", "min": 1, "max": 1 },
    { "name": "shift-3", "from": "2024-01-03T08:00:00", "to": "2024-01-03T16:00:00", "min": 1, "max": 1 }
  ],
  "assignments": [
    { "employee": "Alice", "shift": "shift-1", "locked": true },
    { "employee": "Bob", "shift": "shift-2", "locked": true }
  ]
}
Locked assignments are treated as hard constraints. If they conflict with other hard constraints (e.g., skills, availability), the solution becomes infeasible.

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Assignment Properties

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shift
string
required
Name of the shift to assign
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employee
string
required
Name of the employee to assign
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locked
boolean
default:"false"
When true, the solver cannot modify this assignment

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Mixed Locking

Combine locked and unlocked assignments for partial replanning: 
{
  "assignments": [
    { "employee": "Alice", "shift": "shift-1", "locked": true },
    { "employee": "Bob", "shift": "shift-2", "locked": false },
    { "employee": "Carol", "shift": "shift-3", "locked": false }
  ]
}
Alice stays on shift-1. Bob and Carol’s assignments serve as suggestions that the solver may improve.

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Best Practices

  • Large problems where finding any solution is slow
  • Incremental changes to existing schedules
  • Testing “what-if” scenarios from a known state
  • Employee has confirmed the shift
  • Contractual obligations require specific assignments
  • External constraints not modeled in the API
  • Don’t lock assignments that violate skills or availability
  • Leave flexibility for the solver to optimize
  • Use locked: false for preferences, locked: true only for requirements