Menu
When I query a database and receive a (forward-only, read-only) ResultSet back, the ResultSet acts like a list of database rows.
I am trying to find some way to treat this ResultSet like a Scala Stream. This will allow such operations as filter, map, etc., while not consuming large amounts of RAM.
I implemented a tail-recursive method to extract the individual items, but this requires that all items be in memory at the same time, a problem if the ResultSet is very large:
// Iterate through the result set and gather all of the String values into a list // then return that list @tailrec def loop(resultSet: ResultSet, accumulator: List[String] = List()): List[String] = { if (!resultSet.next) accumulator.reverse else { val value = resultSet.getString(1) loop(resultSet, value +: accumulator) } } 
463
getString(String columnLabel) Retrieves the value of the designated column in the current row of this ResultSet object as a String in the Java programming language. Time. getTime(int columnIndex) Retrieves the value of the designated column in the current row of this ResultSet object as a java.
It is a constant of the ResultSet class representing the concurrency mode for a ResultSet object that may be updated. In general, you will pass this as a value to the createStatement() method.
An SQL result set is a set of rows from a database, as well as metadata about the query such as the column names, and the types and sizes of each column. Depending on the database system, the number of rows in the result set may or may not be known.
The field ResultSet. CONCUR_UPDATABLE creates a ResultSet object that can be updated while CONCUR_READ_ONLY creates a ResultSet that cannot be updated but only it can be read. The problem that you cannot see any changes that you made in the database table is because you are using read only type ResultSet.
I didn't test it, but why wouldn't it work?
new Iterator[String] { def hasNext = resultSet.next() def next() = resultSet.getString(1) }.toStream If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
