Cassandra createSliceQuery clarification

Question

I'm trying to retrieve all columns of a row in Cassandra using Thrift 1.0 lib. I found some examples by Googling , in particular:

SliceQuery<String, String, String> sliceQuery = hectorTemplate.createSliceQuery(
    StringSerializer.get(), StringSerializer.get(), StringSerializer.get());
sliceQuery.setColumnFamily("myname");
sliceQuery.setKey("myid");
sliceQuery.setRange(null, null, false, 20);
QueryResult<ColumnSlice<String,String>> queryResult = sliceQuery.execute();
ColumnSlice<String,String> slice = queryResult.get();
List<HColumn<String, String>> retrievedColumns = slice.getColumns();
for (HColumn<String, String> column : retrievedColumns) {
    System.out.println(column.getName() +"::"+ column.getValue());
}

However, I could not find any information on what those parameters and types in Hector objects are??

For example, here:

SliceQuery<String, String, String> 

• all types here are String - what are they types of? Column name type? column value types?

Then, we specify parameters to the createSliceQuery():

hectorTemplate.createSliceQuery(
    StringSerializer.get(), StringSerializer.get(), StringSerializer.get());

Again - what are those serializers for? why are there only 3 serializers - is if for the first and last column, and something else? What if I get many columns, how do I specify serializers for them?

Then, we retrieve

List<HColumn<String, String>> 

-- again, what are these String types for? If I have a column of type BytesType - where do I specify that?

If there are some decent API docs (not just method signatures with no explanation of what their parameters are) - could you point me to them?

thanks! Marina

Answer 1

In case SliceQuery<K, C, V>, here are the type parameters:

K -- The type of the key

C -- The type of the column name

V -- The type of the column value

Again in case of HColumn<N,V>, type parameters are

N -- The type of the column name

V -- The type of the column value

Similar the case of createSliceQuery