Package com.inductiveautomation.ignition.gateway.sqltags.history.query

Interface HistoryQueryExecutor

All Known Implementing Classes:
AbstractHistoryLoader, AbstractHistoryQueryExecutor, AggregateHistoryQueryExecutor, ErroredQueryExecutor, RemoteTagHistoryQueryExecutor
public interface HistoryQueryExecutor
This is a running query executed by a tag history provider. It will be created by the history provider, and use by the query manager. In general, the execution will go from top to bottom:
  1. initialize() - The query will load information needed for the query. After this call, it is expected that the column nodes will be filled in with their correct data types, or error qualities if bad.
  2. startReading() - The query process will start
  3. While hasMore() : processData()
  4. endReading()

The processData call is allowed to process as much as it wants, but the idea is that it should only process the minimum necessary, to minimize the memory overhead of the query. After each process, the query executor will examine the columns for processed values, and write a result row to the streaming dataset, if possible.

When no more data is available (or the query is canceled), endReading will be called to clean up resources.

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    endReading()
    If startReading was called, this function must be called (that is, it should be in a finally block).
    List<? extends HistoryNode>
    getColumnNodes()
    Returns the HistoryNodes of this executor.
    int
    getEffectiveWindowSizeMS()
    When "natural" results are requested, this will be called to let the query executors say what they think "natural" means.
    boolean
    hasMore()
    Returns TRUE if there is more data available to be written on call to processData()
    void
    initialize()
    Initializes the query, performing any actions necessary to get the information required to run the query.
    long
    nextTime()
    The timestamp of the next value.
    long
    processData()
    Puts the next value(s) into the appropriate column, returning the latest timestamp loaded, or -1 if no data was loaded.
    void
    startReading()
    Begins reading data.

  • Method Details

    • initialize

      void initialize() throws Exception
      Initializes the query, performing any actions necessary to get the information required to run the query.
      Throws:
      Exception

    • getColumnNodes

      List<? extends HistoryNode> getColumnNodes()
      Returns the HistoryNodes of this executor. There MUST be one for every tag path, and they must be in the same order as the paths provided to the executor when it was created. Also, these values must be available as soon as the executor is created. However, they won't be consulted for their data type until after initialize is called, so the normal procedure is to create and return DelegatingHistoryNodes, which get filled in later.

    • getEffectiveWindowSizeMS

      int getEffectiveWindowSizeMS()
      When "natural" results are requested, this will be called to let the query executors say what they think "natural" means. If a query executor does not support natural results, it should return -1. If all of the query executors return -1, a raw query will be performed.

    • startReading

      void startReading() throws Exception
      Begins reading data. IMPORTANT: endReading should always be called at some point after calling startReading.
      Throws:
      Exception

    • endReading

      void endReading()
      If startReading was called, this function must be called (that is, it should be in a finally block).

    • hasMore

      boolean hasMore()
      Returns TRUE if there is more data available to be written on call to processData()

    • nextTime

      long nextTime()
      The timestamp of the next value. -1 if no value is available.

    • processData

      long processData() throws Exception
      Puts the next value(s) into the appropriate column, returning the latest timestamp loaded, or -1 if no data was loaded.
      Throws:
      Exception