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1 : part of flutter_data; 2 : 3 : /// A [Relationship] that models a to-one ownership. 4 : /// 5 : /// Example: A book that belongs to an author 6 : /// ``` 7 : /// class Book with DataModel<Book> { 8 : /// @override 9 : /// final int id; 10 : /// final String title; 11 : /// final BelongsTo<Author> author; 12 : /// 13 : /// Todo({this.id, this.title, this.author}); 14 : /// } 15 : ///``` 16 : class BelongsTo<E extends DataModel<E>> extends Relationship<E, E> { 17 : /// Creates a [BelongsTo] relationship, with an optional initial [E] model. 18 : /// 19 : /// Example: 20 : /// ``` 21 : /// final author = Author(name: 'JK Rowling'); 22 : /// final book = Book(id: 1, author: BelongsTo(author)); 23 : /// ``` 24 : /// 25 : /// See also: [DataModelRelationshipExtension<E>.asBelongsTo] 26 2 : BelongsTo([final E model]) : super(model != null ? {model} : null); 27 : 28 1 : BelongsTo._(String key, bool _wasOmitted) 29 1 : : super._(key != null ? {key} : {}, _wasOmitted); 30 : 31 : /// For internal use with `json_serializable`. 32 1 : factory BelongsTo.fromJson(final Map<String, dynamic> map) { 33 2 : final key = map['_'][0] as String; 34 : if (key == null) { 35 2 : final wasOmitted = map['_'][1] as bool; 36 1 : return BelongsTo._(null, wasOmitted); 37 : } 38 1 : return BelongsTo._(key, false); 39 : } 40 : 41 : /// Obtains the single [E] value of this relationship (`null` if not present). 42 2 : E get value => safeFirst; 43 : 44 : /// Sets the single [E] value of this relationship, replacing any previous [value]. 45 : /// 46 : /// Passing in `null` will remove the existing value from the relationship. 47 1 : set value(E value) { 48 : if (value != null) { 49 1 : if (super.isNotEmpty) { 50 2 : super.remove(this.value); 51 : } 52 1 : super.add(value); 53 : } else { 54 2 : super.remove(this.value); 55 : } 56 2 : assert(length <= 1); 57 : } 58 : 59 : /// Returns the [value]'s `key` 60 1 : @protected 61 : @visibleForTesting 62 2 : String get key => super.keys.safeFirst; 63 : 64 : /// Returns a [StateNotifier] which emits the latest [value] of 65 : /// this [BelongsTo] relationship. 66 1 : @override 67 : StateNotifier<E> watch() { 68 6 : return _graphEvents.where((e) => e.isNotEmpty).map((e) { 69 4 : return e.last.type == DataGraphEventType.removeNode ? null : value; 70 : }); 71 : } 72 : 73 0 : @override 74 0 : String toString() => 'BelongsTo<$E>($value)'; 75 : } 76 : 77 : extension DataModelRelationshipExtension<T extends DataModel<T>> 78 : on DataModel<T> { 79 : /// Converts a [DataModel<T>] into a [BelongsTo<T>]. 80 : /// 81 : /// Equivalent to using the constructor as `BelongsTo(model)`. 82 2 : BelongsTo<T> get asBelongsTo => BelongsTo<T>(this as T); 83 : }