电梯箱类超过22个参数 [英] Lift Case Class Exceeding 22 Arguments

问题描述

使用Lift，我试图提取"我的JSON(获取其案例类表示).

Using Lift, I'm trying to "extract" (get a case class representation of) my JSON.

val json: JValue = getJson()
case class BigObj(name: String, age: Int, ...)
json.extract[BigObj]

当使用超过22个参数时，我得到一个JVM运行时异常，即case类不能超过22个参数.

When using more than 22 arguments, I get a JVM run-time exception that case classes cannot exceed 22 arguments.

如何解决此限制?

推荐答案

如前所述，您不能显式地克服case类的限制，但是可以在没有case类的情况下使用extract方法.请参阅此示例，我通过REPL进行了验证:

As has been mentioned, you can't overcome that limit with a case class explicitly, however you can use the extract method without a case class. See this example, which I ran through REPL to verify:

scala> import net.liftweb.json._
import net.liftweb.json._

scala> implicit val formats = net.liftweb.json.DefaultFormats
formats: net.liftweb.json.DefaultFormats.type = net.liftweb.json.DefaultFormats$@734784c4

scala> val json = parse(""" {
     |           "v1": "Test1",
     |           "v2": "Test2",
     |           "v3": "Test3",
     |           "v4": "Test4",
     |           "v5": "Test5",
     |           "v6": "Test6",
     |           "v7": "Test7",
     |           "v8": "Test8",
     |           "v9": "Test9",
     |           "v10": "Test10",
     |           "v11": "Test11",
     |           "v12": "Test12",
     |           "v13": "Test13",
     |           "v14": "Test14",
     |           "v15": "Test15",
     |           "v16": "Test16",
     |           "v17": "Test17",
     |           "v18": "Test18",
     |           "v19": "Test19",
     |           "v20": "Test20",
     |           "v21": "Test21",
     |           "v22": "Test22",
     |           "v23": "Test23"
     | } """)
json: net.liftweb.json.JValue = JObject(List(JField(v1,JString(Test1)), JField(v2,JString(Test2)), JField(v3,JString(Test3)), JField(v4,JString(Test4)), JField(v5,JString(Test5)), JField(v6,JString(Test6)), JField(v7,JString(Test7)), JField(v8,JString(Test8)), JField(v9,JString(Test9)), JField(v10,JString(Test10)), JField(v11,JString(Test11)), JField(v12,JString(Test12)), JField(v13,JString(Test13)), JField(v14,JString(Test14)), JField(v15,JString(Test15)), JField(v16,JString(Test16)), JField(v17,JString(Test17)), JField(v18,JString(Test18)), JField(v19,JString(Test19)), JField(v20,JString(Test20)), JField(v21,JString(Test21)), JField(v22,JString(Test22)), JField(v23,JString(Test23))))

scala> class MyLargeArgClass(val v1:String, val v2:String, val v3:String, val v4:String, val v5:String, val v6:String, val v7:String, val v8:String, val v9:String, val v10:String, val v11:String, val v12:String, val v13:String, val v14:String, val v15:String, val v16:String, val v17:String, val v18:String, val v19:String, val v20:String, val v21:String, val v22:String, val v23:String) {
     | 
     |   override def toString = "MyLargeArgClass(%s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s)".format(v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20, v21, v22, v23)
     | 
     | }
defined class MyLargeArgClass

scala> json.extract[MyLargeArgClass]
res0: MyLargeArgClass = MyLargeArgClass(Test1, Test2, Test3, Test4, Test5, Test6, Test7, Test8, Test9, Test10, Test11, Test12, Test13, Test14, Test15, Test16, Test17, Test18, Test19, Test20, Test21, Test22, Test23)

然后从类返回JSON

And then going back from the class to JSON

scala> Extraction.decompose(res0)
res1: net.liftweb.json.JValue = JObject(List(JField(v1,JString(Test1)), JField(v2,JString(Test2)), JField(v3,JString(Test3)), JField(v4,JString(Test4)), JField(v5,JString(Test5)), JField(v6,JString(Test6)), JField(v7,JString(Test7)), JField(v8,JString(Test8)), JField(v9,JString(Test9)), JField(v10,JString(Test10)), JField(v11,JString(Test11)), JField(v12,JString(Test12)), JField(v13,JString(Test13)), JField(v14,JString(Test14)), JField(v15,JString(Test15)), JField(v16,JString(Test16)), JField(v17,JString(Test17)), JField(v18,JString(Test18)), JField(v19,JString(Test19)), JField(v20,JString(Test20)), JField(v21,JString(Test21)), JField(v22,JString(Test22)), JField(v23,JString(Test23))))

不必覆盖toString-我只需要查看要添加的数据即可.但是，由于它不是case class，因此您将丢失一些它附带的自动方法.因此，如果需要将其放在HTTP会话中，则可能要实现Serializable.对于模式匹配，您需要unapply方法，等等...

Overriding the toString wasn't necessary - I just needed to see what data was being added. However, since this is not a case class, you will lose some of the automatic methods that come with it. So, if you need to put it in an HTTP Session, you may want to implement Serializable. For pattern matching, you'd need an unapply method, etc...

您还应该能够使用formats来指定自己的其他规则，以便从JSON解析和提取数据.

You should also be able to use formats to specify your own additional rules for parsing and extracting data from your JSON.

这篇关于电梯箱类超过22个参数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！