{"id":3365,"date":"2016-03-12T21:36:14","date_gmt":"2016-03-12T21:36:14","guid":{"rendered":"http:\/\/www.garysieling.com\/blog\/?p=3365"},"modified":"2016-03-12T21:36:14","modified_gmt":"2016-03-12T21:36:14","slug":"scala-while-comprehension","status":"publish","type":"post","link":"https:\/\/www.garysieling.com\/blog\/scala-while-comprehension\/","title":{"rendered":"Scala: while comprehension"},"content":{"rendered":"

In scala, you can do for comprehensions like so:<\/p>\n

\nimport scala.collection.JavaConverters._\n\nfor (x <- myCollection) \n  yield x.someFunction\n<\/pre>\n
Weirdly you can't do this:<\/p>\n
\nwhile (myCollection.hasNext) \n  yield x.next\n<\/pre>\n
This is a common problem with JDBC - ideally the language should let you do this:<\/p>\n
\nval query = \"\"\"\n  | select col1, col2 from my_table;\n\"\"\"\n\nval resultSet = runQuery(query)\nval results: Iterable[Iterable[String]] =\n  while (resultSet.hasNext) \n    resultSet.columns.map(\n      (columnName) => \n        resultSet.get(columnName)\n    )\n<\/pre>\n
Obviously this doesn't work, or you wouldn't be here.<\/p>\n
To do this the scala way, you can use \"Iterator.continually\", like so:<\/p>\n
\nimport scala.collection.JavaConverters._\n\nval data =\n  Iterator.continually {\n    resultSet.next()\n  }.takeWhile(\n    (x) => x\n  ).map(\n    (x) => {\n      resultSet.getColumnNames.asScala.map(\n        (x) => resultSet.getString(x)\n      )\n    }\n  )\n<\/pre>\n
This will give you the dataset you wanted - you can also remove the types from the above example, they are included so that this is easier to understand.<\/p>\n
You can also wrap the above command in a try {}. If you do this, you may wish to realize the results right away, by adding a \".toList\" at the end of the collection, so that you don't hold on to an iterator that is operating on a closed database connection.<\/p>\n","protected":false},"excerpt":{"rendered":"
In scala, you can do for comprehensions like so: import scala.collection.JavaConverters._ for (x<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"footnotes":""},"categories":[4],"tags":[480,485,486],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t