[Scala] play架構使用tree結構json « Terrence的宅宅幻想
阿新 • • 發佈：2018-12-29
今天想用樹狀結構去顯示Presto裡面的table source
使用的API是吃json的格式
var tree = [
{
text: "Parent 1",
nodes: [
{
text: "Child 1",
nodes: [
{
text: "Grandchild 1"
},
{
text: "Grandchild 2"
}
]
},
{
text: "Child 2"
}
]
},
{
text: "Parent 2"
},
{
text: "Parent 3"
},
{
text: "Parent 4"
},
{
text: "Parent 5"
}
];
對應到目前開發中的scala play project，就面臨到了如何做格式轉換的問題
目前是將資料庫裡面catalog, schema, table等資訊用TableData這個物件封裝起來
case class TableData(catalog:String, schema:String, table: String) def listTables: List[TableData] = { ... //result example (mysql, database1, table1) (mysql, database1, table2) (hive, schema1, table3)
ㄧ開始想的很簡單，轉成list/map的組合用內建的toJson函式去解就好了
val tablesTree = listTables.groupBy(_.catalog).toList.collect{ case (c, table) => Map("text" -> c, "nodes" -> table.groupBy(_.schema).toList.collect{ case (s, table) => Map("text" -> s, "nodes" -> table.map(x => Map("text"-> x.table))) }) } Ok(toJson(tablesTree))
但是馬上就出了問題
No Json serializer found for type List[scala.collection.immutable.Map[String,java.io.Serializable]]. Try to implement an implicit Writes or Format for this type.
當單純使用List/Map的時候其實沒問題，但這邊問題出在Map使用了不同的data type當value
Map(text -> String, nodes -> List)
不同的data type當value時, scala直接把它統一看成java.io.Serializable
這樣怎麼辦呢？只好自己製作json writer
先自制一個TreeNode資料結構, 然後將原先List/Map資料轉換改成TreeNode的格式
case class TreeNode(text:String, nodes:List[TreeNode]) val tablesTree = tables.groupBy(_.catalog).toList.collect{ case (c, table) => new TreeNode(c, table.groupBy(_.schema).toList.collect{ case (s, table) => new TreeNode(s, table.map(x => new TreeNode(x.table, List()))) }) }
之後補上一段轉換json的code, 使用lazyWrite做recursive的tree結構處理
import play.api.libs.functional.syntax._ import play.api.libs.json._ case class TreeNode(text:String, nodes:List[TreeNode]) implicit val TreeNodeWrite:Writes[TreeNode] = ( (__ \ "text").write[String] ~ (__ \ "nodes").lazyWrite(Writes.traversableWrites[TreeNode](TreeNodeWrite)) )(unlift(TreeNode.unapply)) val tablesTree = tables.groupBy(_.catalog).toList.collect{ case (c, table) => new TreeNode(c, table.groupBy(_.schema).toList.collect{ case (s, table) => new TreeNode(s, table.map(x => new TreeNode(x.table, List()))) }) }
但是這時候跑出了一段錯誤訊息
forward reference extends over definition of value
原來問題出在TreeNodeWrite在宣告的同時就讓它被lazyWrite使用出的錯誤
後來找到的解法是可用 lazy 去關鍵字去解決這問題
import play.api.libs.functional.syntax._ import play.api.libs.json._ case class TreeNode(text:String, nodes:List[TreeNode]) implicit lazy val TreeNodeWrite:Writes[TreeNode] = ( (__ \ "text").write[String] ~ (__ \ "nodes").lazyWrite(Writes.traversableWrites[TreeNode](TreeNodeWrite)) )(unlift(TreeNode.unapply)) val tablesTree = tables.groupBy(_.catalog).toList.collect{ case (c, table) => new TreeNode(c, table.groupBy(_.schema).toList.collect{ case (s, table) => new TreeNode(s, table.map(x => new TreeNode(x.table, List()))) }) } Ok(toJson(tablesTree))
加上延遲處理的判斷之後就可以順利執行了
＊補充
這段code還有個小問題，就是最後一定會把nodes屬性傳給前端
前端需要一個處理把空的nodes給移除掉
$.getJSON("presto/listTables", function(json){ (function filter(obj) { $.each(obj, function(key, value){ //移除空值 if (value === "" || value === null || value.length == 0){ delete obj[key]; } else if (Object.prototype.toString.call(value) === '[object Object]') { filter(value); } else if (Array.isArray(value)) { value.forEach(function (el) { filter(el); }); } }); })(json); $('#tree').treeview({data: json}); });