ReadQuery (apache-cassandra API)

All Known Subinterfaces:

PartitionRangeReadQuery, SinglePartitionReadQuery

All Known Implementing Classes:

PartitionRangeReadCommand, ReadCommand, SinglePartitionReadCommand, SinglePartitionReadCommand.Group, SinglePartitionReadQuery.Group, VirtualTablePartitionRangeReadQuery, VirtualTableReadQuery, VirtualTableSinglePartitionReadQuery, VirtualTableSinglePartitionReadQuery.Group
```
public interface ReadQuery
```
Generic abstraction for read queries.

Method Summary

All Methods Static Methods Instance Methods Abstract Methods Default Methods
Modifier and Type	Method and Description
`ColumnFilter`	`columnFilter()` A filter on which (non-PK) columns must be returned by the query.
`static ReadQuery`	`empty(TableMetadata metadata)`
`PartitionIterator`	`execute(ConsistencyLevel consistency, ClientState clientState, long queryStartNanoTime)` Executes the query at the provided consistency level.
`PartitionIterator`	`executeInternal(ReadExecutionController controller)` Execute the query for internal queries (that is, it basically executes the query locally).
`UnfilteredPartitionIterator`	`executeLocally(ReadExecutionController executionController)` Execute the query locally.
`ReadExecutionController`	`executionController()` Starts a new read operation.
`QueryPager`	`getPager(PagingState pagingState, ProtocolVersion protocolVersion)` Returns a pager for the query.
`default boolean`	`isEmpty()` Whether this query is known to return nothing upfront.
`DataLimits`	`limits()` The limits for the query.
`default void`	`maybeValidateIndex()` If the index manager for the table determines that there's an applicable 2i that can be used to execute this query, call its (optional) validation method to check that nothing in this query's parameters violates the implementation specific validation rules.
`TableMetadata`	`metadata()` The metadata for the table this is a query on.
`int`	`nowInSec()` The time in seconds to use as "now" for this query.
`RowFilter`	`rowFilter()` Filters/Resrictions on CQL rows.
`boolean`	`selectsClustering(DecoratedKey key, Clustering<?> clustering)`
`boolean`	`selectsFullPartition()` Checks if this `ReadQuery` selects full partitions, that is it has no filtering on clustering or regular columns.
`boolean`	`selectsKey(DecoratedKey key)`

- Method Detail
  - empty
```
static ReadQuery empty(TableMetadata metadata)
```
  - metadata
```
TableMetadata metadata()
```
    The metadata for the table this is a query on.
    
    Returns:
    
    the metadata for the table this is a query on.
  - executionController
```
ReadExecutionController executionController()
```
    Starts a new read operation.
    This must be called before executeInternal and passed to it to protect the read. The returned object must be closed on all path and it is thus strongly advised to use it in a try-with-ressource construction.
    
    Returns:
    
    a newly started execution controller for this ReadQuery.
  - execute
```
PartitionIterator execute(ConsistencyLevel consistency,
                          ClientState clientState,
                          long queryStartNanoTime)
                   throws RequestExecutionException
```
    Executes the query at the provided consistency level.
    
    Parameters:
    
    consistency - the consistency level to achieve for the query.
    
    clientState - the ClientState for the query. In practice, this can be null unless consistency is a serial consistency.
    
    Returns:
    
    the result of the query.
    
    Throws:
    
    RequestExecutionException
  - executeInternal
```
PartitionIterator executeInternal(ReadExecutionController controller)
```
    Execute the query for internal queries (that is, it basically executes the query locally).
    
    Parameters:
    
    controller - the ReadExecutionController protecting the read.
    
    Returns:
    
    the result of the query.
  - executeLocally
```
UnfilteredPartitionIterator executeLocally(ReadExecutionController executionController)
```
    Execute the query locally. This is similar to executeInternal(ReadExecutionController) but it returns an unfiltered partition iterator that can be merged later on.
    
    Parameters:
    
    executionController - the ReadExecutionController protecting the read.
    
    Returns:
    
    the result of the read query.
  - getPager
```
QueryPager getPager(PagingState pagingState,
                    ProtocolVersion protocolVersion)
```
    Returns a pager for the query.
    
    Parameters:
    
    pagingState - the PagingState to start from if this is a paging continuation. This can be null if this is the start of paging.
    
    protocolVersion - the protocol version to use for the paging state of that pager.
    
    Returns:
    
    a pager for the query.
  - limits
```
DataLimits limits()
```
    The limits for the query.
    
    Returns:
    
    The limits for the query.
  - selectsKey
```
boolean selectsKey(DecoratedKey key)
```
    Returns:
    
    true if the read query would select the given key, including checks against the row filter, if checkRowFilter is true
  - selectsClustering
```
boolean selectsClustering(DecoratedKey key,
                          Clustering<?> clustering)
```
    Returns:
    
    true if the read query would select the given clustering, including checks against the row filter, if checkRowFilter is true
  - nowInSec
```
int nowInSec()
```
    The time in seconds to use as "now" for this query.
    We use the same time as "now" for the whole query to avoid considering different values as expired during the query, which would be buggy (would throw of counting amongst other things).
    
    Returns:
    
    the time (in seconds) to use as "now".
  - selectsFullPartition
```
boolean selectsFullPartition()
```
    Checks if this ReadQuery selects full partitions, that is it has no filtering on clustering or regular columns.
    
    Returns:
    
    true if this ReadQuery selects full partitions, false otherwise.
  - rowFilter
```
RowFilter rowFilter()
```
    Filters/Resrictions on CQL rows.
    This contains the restrictions that are not directly handled by the ClusteringIndexFilter. More specifically, this includes any non-PK column restrictions and can include some PK columns restrictions when those can't be satisfied entirely by the clustering index filter (because not all clustering columns have been restricted for instance). If there is 2ndary indexes on the table, one of this restriction might be handled by a 2ndary index.
    
    Returns:
    
    the filter holding the expression that rows must satisfy.
  - columnFilter
```
ColumnFilter columnFilter()
```
    A filter on which (non-PK) columns must be returned by the query.
    
    Returns:
    
    which columns must be fetched by this query.
  - isEmpty
```
default boolean isEmpty()
```
    Whether this query is known to return nothing upfront.
    This is overridden by the ReadQuery created through empty(TableMetadata), and that's probably the only place that should override it.
    
    Returns:
    
    if this method is guaranteed to return no results whatsoever.
  - maybeValidateIndex
```
default void maybeValidateIndex()
```
    If the index manager for the table determines that there's an applicable 2i that can be used to execute this query, call its (optional) validation method to check that nothing in this query's parameters violates the implementation specific validation rules.

Interface ReadQuery

Method Summary

Method Detail

empty

metadata

executionController

execute

executeInternal

executeLocally

getPager

limits

selectsKey

selectsClustering

nowInSec

selectsFullPartition

rowFilter

columnFilter

isEmpty

maybeValidateIndex