在Slick官方文檔中描述：連接后臺數(shù)據(jù)庫后，需要通過定義Projection，即def * 來進行具體庫表列column的選擇和排序。通過Projection我們可以選擇庫表中部分列、也可以增加一些自定義列computed column。具體來說Projection提供了數(shù)據(jù)庫表列與Scala值的對應(yīng)。例如def * = (column1,column2)把庫表的column1和column2與(Int,String)對應(yīng)，column1[Int]，column2[String]。也可以說是與定義column的類參數(shù)進行對應(yīng)。從Slick源代碼中我們可以找到Projection定義：
abstract class AbstractTable[T](val tableTag: Tag, val schemaName: Option[String], val tableName: String) extends Rep[T] { /** The client-side type of the table as defined by its * projection */
type TableElementType
... /** The * projection of the table used as default for queries and inserts.
* Should include all columns as a tuple, HList or custom shape and optionally
* map them to a custom entity type using the <> operator.
* The `ProvenShape` return type ensures that
* there is a `Shape` available for translating between the `Column`-based
* type in * and the client-side type without `Column` in the table's type
* parameter. */
def * : ProvenShape[T]
...
}
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