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

ohhhhh.. hold on. hold on please. can you ask one question at a time? Rather select an API, may be astyanax, hector, native binary driver or pelops and can ask question based on them? — abhi
This is a good question about the Hector API (I don't understand why it is not clear to you which API is in question). Indeed, the Hector javadoc does not seem to document the generic types. — Tom
For what it's worth, have a look at Pelops. It's an excellently designed and documented Cassandra client library. I never understood why most people go for Hector. — Tom
Abhi, Tom - yes, my questions are about the Hector API. Why most people use it - not sure, maybe because when you Google for examples of Cassandra JAva-based clients, it is the one that shows up most, even though their API docs are a joke - all they show is method signatures, with zero info about what those parameters actually mean... — Marina
@abhi this is really just one question, I probably expressed it in too many words :) - whether somebody could either provide or point to information about the meaning of parameters and their types in Hector APIs. — Marina

abhi abhi · Accepted Answer · 2013-05-09T05:01:11

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

Cassandra createSliceQuery clarification

1 Answers