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Android Room:创建一对一关系实体

android-room entity sqlite android

noloman amram99 · 技术社区 · 4 年前

我正在用Room和三个表(作业、标签、类别)创建一个小项目。

基本上:

作业属于(或只有)1个类别,但作业可以有0..N个标签。
一个类别有0..N个作业。
一个标签有0..N个作业。

我在尝试对所有数据进行建模时遇到了一些困难,尤其是在实体之间的关系方面。更具体地说,我有:

fun JobListing.toJobEntityList(): List<JobEntity> {
    val jobEntityList = mutableListOf<JobEntity>()
    this.jobs.take(50).forEach { job: Job ->
        jobEntityList.add(
            JobEntity(
                jobId = job.id,
                title = job.title,
                url = job.url,
                companyName = job.companyName,
                jobType = job.jobType,
                publicationDate = job.publicationDate,
                relocation = job.candidateRequiredLocation,
                salary = job.salary
            )
        )
    }
    return jobEntityList
}

当我从网络获取数据时,会调用此扩展函数,因此我可以将其转换为实体并将其存储在我的数据库中。我基本上是在创造一个 JobEntity ,但作业应关联1个类别和0..N个标签。问题是,我不知道如何添加与作业及其类别和标签之间的关系相关的数据。

这是我的 工作实体 类别:

@Entity(
    tableName = "Jobs",
    indices = [
        Index("id", unique = true)
    ]
)
data class JobEntity(
    @PrimaryKey @ColumnInfo(name = "id") val jobId: Int,
    @ColumnInfo(name = "title") val title: String,
    @ColumnInfo(name = "url") val url: String,
    @ColumnInfo(name = "company_name") val companyName: String,
    @ColumnInfo(name = "job_type") val jobType: String,
    @ColumnInfo(name = "publication_date") val publicationDate: String,
    @ColumnInfo(name = "candidate_required_location") val relocation: String,
    @ColumnInfo(name = "salary") val salary: String
)

提前感谢!

1 回复 | 直到 4 年前

Rustam Samandarov 4 年前

嗨,你应该这样建模你的数据库:

职位_类别
标签
作业(添加category_id字段,并向category表添加1个外键引用)
Job_Tags(添加tag_id、Job_id字段,并添加2个引用类别和作业表的外键)

@Entity(tableName = "Category")
data class CategoryEntity(
    @PrimaryKey @ColumnInfo(name = "id") val id: Int,
)

@Entity(tableName = "Tags")
data class TagEntity(
    @PrimaryKey @ColumnInfo(name = "id") val id: Int,
)

@Entity(
    tableName = "Jobs",
    foreignKeys = [ForeignKey(entity = CategoryEntity::class, parentColumns = ["id"], childColumns = ["categoryid"])]
)
data class JobEntity(
    @PrimaryKey @ColumnInfo(name = "id") val id: Int,
    @ColumnInfo(name = "categoryid", index = true) val categoryid: Int,
    // ... other fields
)
@Entity(
    tableName = "JobTags",
    foreignKeys = [
        ForeignKey(entity = TagEntity::class, parentColumns = ["id"], childColumns = ["tagId"]),
        ForeignKey(entity = JobEntity::class, parentColumns = ["id"], childColumns = ["jobId"]),
    ]
)
data class JobTagEntity(
    @PrimaryKey @ColumnInfo(name = "id") val id: Int,
    @ColumnInfo(name = "tagId", index = true) val tagId: Int,
    @ColumnInfo(name = "jobId", index = true) val jobId: Int,
)