android - 如何从 firebase db android 中的多对多关系获取完整数据？

Question

我有一个属于学校的类(class)，这个类(class)有老师和学生，他们都有名字，可能还有电话号码，我想获得类(class)的完整数据但首先，你能给我一些建议吗，从以下 Dbs 中什么是最好的性能和维护:

第一个

 "schools":{
   "school1":{
     "class1":{
       "name":"SC1",
       "teachers":[{
         "name":"T1"
       }, {
         "name":"T2"
       }],
       "students":[
         {"name":"S1"},
         {"name":"S2"}
         ]
     }
   }
.
.
.
.
.
.
.

 }

和第二个

  "school":{
    "school1":{
      "name":"SC1"
    },
    "school2":{
      "name":"SC2"
    }
  },
  "classes": {
    "class1": {
      "name": "C1"
    },
    "class2": {
      "name": "C2"
    }
  },
  "students": {
    "student1": {
      "name": "S1",
      "phone":"123456789"
    },
    "student2": {
      "name": "S2",
      "phone":"123456789"
    },
    "student3": {
      "name": "S3",
      "phone":"123456789"
    },
    "student4": {
      "name": "S4",
      "phone":"123456789"
    }
  },
  "teachers": {
    "student1": {
      "name": "T1",
      "phone":"123456789"
    },
    "student2": {
      "name": "T2",
      "phone":"123456789"
    },
    "student3": {
      "name": "T3",
      "phone":"123456789"
    },
    "student4": {
      "name": "T4",
      "phone":"123456789"
    }
  },
  "classes_enrollments": {
    "class1": {
      "teacher1": true,
      "teacher3": true,
      "student1": true,
      "student2": true
    },
    "class2": {
      "teacher2": true,
      "teacher4": true,
      "student3": true,
      "student4": true
    },
    "class3": {
      "teacher1": true,
      "teacher2": true,
      "student3": true,
      "student4": true,
      "student1": true,
      "student2": true
    }
  },
  "student_friends": {
    "student1": {
      "student2": true
    },
    "students2": {
      "student1": true,
      "student3": true
    },
    "students3": {
      "student2": true
    }
  },
  "teacher_friends": {
    "teacher1": {
      "teacher2": true
    },
    "teacher2": {
      "teacher1": true,
      "teacher3": true
    },
    "teacher3": {
      "teacher2": true
    }
  }

关于如何获取类(class)1的完整数据的第二种方式:在哪所学校及其教师和学生的姓名和人数以及他们的姓名和电话

谢谢

Answer 1

我会混合这两者。

为了代码简洁和单个类细节的阅读性能，第二种方案确实会很乱。第一种方案会更好，但有一些改进。

将 teachers 和 students 路径保留在根目录下，就像在第二个方案中一样。

在根目录添加teacher_enrollments和student_enrollments路径，保存每个老师/学生关联的类(class)id。

不要将类(class)教师和学生保存为类(class)内部的数组，而是使用映射，类似于您在根 teachers 和 students 路径中保存的内容。

这样，当您从根路径编辑教师时，您还可以从注册路径中获取所有相关类(class)(id)的列表，并对这些类(class)进行多路径更新，以更新每个相关类(class)的教师/学生详细信息。

如果您有大量数据，您可能希望为类(class)摘要维护一个单独的路径，以便您可以轻松地显示类(class)列表，而无需下载所有包含的教师和学生的数据(这些数据将存在在所有这些类(class)中多次)。

当您删除一个类(class)时，您还需要执行多路径更新以删除所有关联的注册。 如果学生和教师的总人数不是太多，您可以删除所有教师/学生的注册。如果你有很多老师/学生，你可以保留你的 classes_enrollments 路径(但在 ids 之前有中间 teachers 和 students)，这样您可以仅使用所需的教师/学生 ID 进行更新。(实际上要简单得多。您在类(class)信息中已经有了教师/学生 ID)

// How to delete a class in JavaScript.
// For Java, use updateChildren() instead of update(),
// and supply it with a HashMap instead of a plain object.
const classToDelete = { id: 'class1', teachers: ..., students: ..., school: ... };
const updateObject = {
  ['classes/'+classToDelete.id]: null },
  ['schools/'+classToDelete.school.id+'/classes/'+classToDelete.id]: null },
};
Object.keys(classToDelete.teachers).forEach(teacherId => {
  updateObject['teachers/'+teacherId +'/classes/'+classToDelete.id] = null;
});
Object.keys(classToDelete.students).forEach(studentId=> {
  updateObject['students/'+studentId+'/classes/'+classToDelete.id] = null;
});
dbRef.update(updateObject);

示例数据库结构(与说明略有不同，但使用相同的概念):

"schools": {
    "school1": {
        "id": "school1",
        "name": "The best school",
        "classes": {
            "class1": {
                "id": "class1",
                "name": "The best class"
            }
        }
    }
},
"classes": {
    "class1": {
        "id": "class1",
        "name": "The best class",
        "teachers": {
            "teacher1": {
                "id": "teacher1",
                "name": "The best teacher",
                "phone": "123"
            }
        },
        "students": {
            "student1": {
                "id": "student1",
                "name": "The best student",
                "phone": "456"
            }
        },
        "school": {
            "id": "school1",
            "name": "The best school"
        }
    }
},
"teachers": {
    "teacher1": {
        "id": "teacher1",
        "name": "The best teacher",
        "phone": "123",
        "classes": {
            "class1": {
                "name": "The best class",
                "school": {
                    "id": "school1",
                    "name": "The best school"
                }
            }
        }
    }
},
"students": {
    "student1": {
        "id": "student1",
        "name": "The best student",
        "phone": "456",
        "classes": {
            "class1": {
                "name": "The best class",
                "school": {
                    "id": "school1",
                    "name": "The best school"
                }
            }
        }
    }
}

祝你好运!