Room 数据库自增长id导致数据插入失败的解决方案

    在Room数据库中，我们定义数据实体类跟数据库表进行一一对应，在定义的表存我们经常会用到自增长的id列，定义了自增长的列，在插入数据时构建数据实体对象时，如果数据实体类中使用了自增长的id列，数据插入时id列的值可以设置为 null (Kotlin，Java中使用默认值），数据库会自动编排id值。但是如果数据实体类中的id列指定了默认值，出现了数据无法插入的问题（笔者经历）。如下代码所示：

// 数据实体定义
@Entity(tableName = "records")
class Record(@ColumnInfo var timeMillisecond: Long, @ColumnInfo var date: String, @ColumnInfo var time: String,
             @ColumnInfo var dateYM: String, @ColumnInfo var chargeAmount: Float, @ColumnInfo var chargeCost: Float,
             @ColumnInfo var mileage: Int, @ColumnInfo var socBefore: Int = 0, @ColumnInfo var socAfter: Int = 0,
             @ColumnInfo var station: String? = null, @ColumnInfo var memo: String? = null,
             @ColumnInfo var extra: String? = null, @ColumnInfo var carId: Long = -1) {
    @PrimaryKey(autoGenerate = true) var id: Long = -1
}

在其自编id时，以上定义的数据实体无法插入数据。

    根据前面提到，问题就出在指定了id列的默认值，导致数据库插入数据时无法编排id导致插入数据失败，但是并不是不能指定默认值，笔者遇到这个问题最终发现是id列的默认值不能为负数。

    如果用Java语言，直接使用默认值即可，或者指定0位id列的默认值。如果使用 Kotlin 语言开发，可将 id 列定义为可空，或者指定默认值为 0.

// 数据实体定义
@Entity(tableName = "records")
class Record(@ColumnInfo var timeMillisecond: Long, @ColumnInfo var date: String, @ColumnInfo var time: String,
             @ColumnInfo var dateYM: String, @ColumnInfo var chargeAmount: Float, @ColumnInfo var chargeCost: Float,
             @ColumnInfo var mileage: Int, @ColumnInfo var socBefore: Int = 0, @ColumnInfo var socAfter: Int = 0,
             @ColumnInfo var station: String? = null, @ColumnInfo var memo: String? = null,
             @ColumnInfo var extra: String? = null, @ColumnInfo var carId: Long = -1) {
    @PrimaryKey(autoGenerate = true) var id: Long = -1
}

// 数据实体定义2
@Entity(tableName = "records")
class Record(@ColumnInfo var timeMillisecond: Long, @ColumnInfo var date: String, @ColumnInfo var time: String,
             @ColumnInfo var dateYM: String, @ColumnInfo var chargeAmount: Float, @ColumnInfo var chargeCost: Float,
             @ColumnInfo var mileage: Int, @ColumnInfo var socBefore: Int = 0, @ColumnInfo var socAfter: Int = 0,
             @ColumnInfo var station: String? = null, @ColumnInfo var memo: String? = null,
             @ColumnInfo var extra: String? = null, @ColumnInfo var carId: Long = -1) {
    @PrimaryKey(autoGenerate = true) var id: Long? = null
}