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# ChangeEffects

The side effects of an applied change set: records removed by a cascade, ids the engine generated, and links or assignments that became inactive. Read it from [`ApplyReport::effects`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/changes/apply-report.md#effects>), returned by [`Project::apply`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/project/project.md#apply>), to keep your own copy of the data in sync with the project.

## Declaration

```rust
#[derive(Clone, Debug, Default, PartialEq)]
pub struct ChangeEffects {
    pub removed_tasks: Vec<Id>,
    pub removed_links: Vec<Id>,
    pub generated_links: Vec<Id>,
    pub dropped_links: Vec<Id>,
    pub removed_assignments: Vec<Id>,
    pub generated_assignments: Vec<Id>,
    pub dropped_assignments: Vec<Id>,
}
```

With the `serde` feature, `ChangeEffects` implements `Serialize` and `Deserialize`, with camelCase field names (`removedTasks`, `generatedLinks`, ...).

Every list holds ids from applied operations only. A rejected operation adds nothing. Ids appear in the order the operations ran. All lists are empty when the change set had no such effect.

## Fields

| Field | Type | Description |
|---|---|---|
| `removed_tasks` | `Vec<`[`Id`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/data/id.md>)`>` | Tasks deleted from the project. |
| `removed_links` | `Vec<`[`Id`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/data/id.md>)`>` | Links deleted from the project. |
| `generated_links` | `Vec<`[`Id`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/data/id.md>)`>` | Ids the engine assigned to added links that had no id. |
| `dropped_links` | `Vec<`[`Id`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/data/id.md>)`>` | Links that became inactive. |
| `removed_assignments` | `Vec<`[`Id`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/data/id.md>)`>` | Assignments deleted from the project. |
| `generated_assignments` | `Vec<`[`Id`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/data/id.md>)`>` | Ids the engine assigned to added assignments that had no id. |
| `dropped_assignments` | `Vec<`[`Id`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/data/id.md>)`>` | Assignments that became inactive. |

### removed_tasks

```rust
pub removed_tasks: Vec<Id>
```

Each task named in `tasks.remove`, followed by all of its descendants, which are removed with it.

### removed_links

```rust
pub removed_links: Vec<Id>
```

Links named in `links.remove`, and links removed because their source or target task was removed.

### generated_links

```rust
pub generated_links: Vec<Id>
```

Ids of added links whose [`LinkAdd::id`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/changes/link-add.md#id>) was `None`. A generated id has the form `$generated_link_1`, `$generated_link_2`, and so on. Use it to update or remove the link later.

### dropped_links

```rust
pub dropped_links: Vec<Id>
```

Links that are still in the project but became inactive because of this change set. Links that were already inactive aren't listed. For the cases that drop a link, see [`LinkData`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/data/link-data.md>).

### removed_assignments

```rust
pub removed_assignments: Vec<Id>
```

Assignments named in `assignments.remove`, and assignments removed because their task or resource was removed. A cascaded assignment that has no id isn't listed.

### generated_assignments

```rust
pub generated_assignments: Vec<Id>
```

Ids of added assignments that had no id. A generated id has the form `$generated_assignment_1`, `$generated_assignment_2`, and so on.

### dropped_assignments

```rust
pub dropped_assignments: Vec<Id>
```

Assignments that are still in the project but became inactive because of this change set. Assignments that were already inactive aren't listed. For the cases that drop an assignment, see [`AssignmentData::task`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/data/assignment-data.md#task>).

## Example

Remove task 1, which takes link 10 with it, and add a link without an id:

```rust
use plen_core::{
    Changes, DateTime, LinkAdd, LinkData, LinkType, Project, ProjectData, SchedulingChanges,
    SolveOptions, TaskData,
};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let start = DateTime::from_ymd_hm(2026, 4, 6, 8, 0).ok_or("invalid date")?;
    let data = ProjectData {
        tasks: vec![
            TaskData { start_date: Some(start), duration: Some(1.0), ..TaskData::new(1) },
            TaskData { start_date: Some(start), duration: Some(2.0), ..TaskData::new(2) },
            TaskData { start_date: Some(start), duration: Some(3.0), ..TaskData::new(3) },
        ],
        links: vec![LinkData {
            id: 10.into(),
            source: 1.into(),
            target: 2.into(),
            link_type: LinkType::Fs,
            lag: 0.0,
            lag_unit: None,
        }],
        ..Default::default()
    };

    let mut project = Project::default();
    project.solve(Some(data), &SolveOptions::default())?;

    let changes = SchedulingChanges {
        tasks: Changes { remove: vec![1.into()], ..Default::default() },
        links: Changes {
            add: vec![LinkAdd {
                id: None,
                source: 2.into(),
                target: 3.into(),
                link_type: LinkType::Fs,
                lag: 0.0,
                lag_unit: None,
            }],
            ..Default::default()
        },
        ..Default::default()
    };

    let effects = project.apply(&changes)?.effects;
    println!("removed tasks: {:?}", effects.removed_tasks); // [Num(1.0)]
    println!("removed links: {:?}", effects.removed_links); // [Num(10.0)]
    println!("new link ids: {:?}", effects.generated_links); // [Str("$generated_link_1")]
    Ok(())
}
```

## Related

- [`ApplyReport`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/changes/apply-report.md>) - carries the effects in `effects`
- [`SchedulingChanges`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/changes/scheduling-changes.md>) - the change set whose operations cause these effects
- [`LinkAdd`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/changes/link-add.md>) - an added link without an id gets a generated one here
- [Data Updates](<https://docs.dhtmlx.com/planning-engine/rust/live-projects/editing-a-project.md>) - shows how to keep a local copy in sync after `apply`