SwiftData中ModelContext的delete(model:)方法失效，级联删除未触发

你的问题出在两个核心点上：

1. 批量删除方法的作用范围限制 #

ModelContext.delete(model:where:)是针对持久化存储的批量删除操作，而你设置了context.autosaveEnabled = false，插入School和Student实例后没有手动调用context.save()——这些实例仅存在于内存上下文，并未写入存储。因此批量删除方法找不到目标实例，自然不会执行删除操作。

2. 双向关系未正确同步 #

虽然你定义了关系的inverse，但自动保存关闭时，SwiftData不会自动将Student实例同步到School的students数组中。这会导致级联删除规则无法触发：即便School被删除，关联的Student也不会被一并删除。

修复后的测试代码 #

import XCTest
import SwiftData

@Model
class School {
    var name: String
    @Relationship(deleteRule: .cascade, inverse: \Student.school)
    var students: [Student]

    init(name: String, students: [Student]) {
        self.name = name
        self.students = students
    }
}

@Model
class Student {
    var name: String
    var school: School

    init(name: String, school: School) {
        self.name = name
        self.school = school
    }
}

final class Test: XCTestCase {
    func testScenario() throws {
        let modelContainer = try ModelContainer(for:
            School.self,
            Student.self
        )
        
        let context = ModelContext(modelContainer)
        context.autosaveEnabled = false
        
        let school = School(name: "school", students: [])
        context.insert(school)
        
        let student1 = Student(name: "1", school: school)
        let student2 = Student(name: "2", school: school)
        context.insert(student1)
        context.insert(student2)
        
        // 手动维护双向关系，确保关联生效
        school.students.append(student1)
        school.students.append(student2)
        
        // 将实例持久化到存储，让批量删除方法能定位到目标
        try context.save()
        
        XCTAssertEqual(try! context.fetchCount(FetchDescriptor<School>()), 1)
        XCTAssertEqual(try! context.fetchCount(FetchDescriptor<Student>()), 2)
        
        // 执行批量删除
        try context.delete(model: School.self)
        // 保存操作触发级联删除并同步到存储
        try context.save()
        
        XCTAssertEqual(try! context.fetchCount(FetchDescriptor<School>()), 0)
        XCTAssertEqual(try! context.fetchCount(FetchDescriptor<Student>()), 0)
    }
}

无需持久化的替代方案 #

如果不想依赖存储，也可以直接查询内存中的实例并逐个删除，这种方式不需要提前save：

// 替换原有的批量删除代码
let schools = try context.fetch(FetchDescriptor<School>())
schools.forEach(context.delete)
// 无需save即可在内存上下文看到删除效果，断言会直接通过

内容的提问来源于stack exchange，提问作者Magnuti