The DataStax documentation says that to page through all data, the following CQL query is useful:
SELECT * FROM test WHERE token(k) > token(42);
Is it possible to build this query using the QueryBuilder? It provides a token method, but that seems to work only on column names, not on values.
Ideally, the value (in the example: 42) is of type Object, just like in the eq/gte/lte functions.
Try using automatic paging with the .fetchSize method. It uses token under the hood:
Automatic paging is introduced Cassandra 2.0. Automatic paging allows the developer to iterate on an entire ResultSet without having to care about its size: some extra rows are fetched as the client code iterate over the results while the old ones are dropped. The amount of rows that must be retrieved can be parameterized at query time. In the Java Driver this will looks like:
Statement stmt = new SimpleStatement("SELECT * FROM images");
stmt.setFetchSize(100);
ResultSet rs = session.execute(stmt);
Source: http://www.datastax.com/dev/blog/client-side-improvements-in-cassandra-2-0
QueryBuilder.fcall("token", value) ;
can solve the problem！
Related
I'm working with the Datastax Node.js driver and I can't figure out when to use a mapper vs. query. Both seem to be able to perform the same CRUD operations.
With a query:
const q = SELECT * FROM mykeyspace.mytable WHERE id='12345';
client.execute(q).then(result => console.log('This is the data', result);
With mapper:
const tableRow = await tableMapper.find({ id: '12345' });
When should I use the mapper over a query and vice versa?
Mapper is a feature from cassandra-driver released in 2018. Using mapper, cassandra-driver can make a map from your cassandra table to an object in nodejs and you can handle in your nodejs application like a set of document.
Using mapper you can make selects or inserts in your database like said in this article:
https://www.datastax.com/blog/2018/12/introducing-datastax-nodejs-mapper-apache-cassandra
With query method, if you need to use or reuse any property from your json you will need to make a Json.Parse().
The short answer is: whatever you find more comfortable.
The Mapper lets you deal with database data as documents (JavaScript objects), builds the CQL query for you, executes the query and maps the results.
On the other hand, the core driver only supports executing CQL queries that you have to write yourself.
What is the equivalent of:
INSERT INTO table (myColumn) VALUES (now())
using the Cassandra object-mapping api?
The #Computed annotation doesnt look like it would work unfortunately.
You can also set the value of your object to a type1 uuid. The jre doesnt have standard function for it but you can use the java driver util, JUG, cassandra-all or even write one yourself. This would be a little different because your setting the time as the time of creation as opposed to coordinator setting time of when it receives the request but with ORM's abstractions you tend to lose some control.
Alternatively there is nothing preventing you from issuing CQL statements while still using the object mapping api. Maybe even adding a query to a method on your object to do it ie:
#Query("UPDATE table SET myColumn = now() WHERE ....")
public ResultSet setNow()
I have a cql query I want to preform. The cql string looks like this:
SELECT * FROM :columnFamilyName WHERE <some_column_name> = :name AND <some_id> = :id;
My application has two layers of abstraction above the datastax driver. In one layer I want to bind the first two parameters and in another layer I'd like to bind the last parameter.
The problem is, if I bind the first two parameters, I get a BoundStatement to which I cannot bind another parameter. Am I missing something? Can it be done?
We're using datastax driver version 2.0.3.
Thanks,
Anatoly.
You should be able to bind any number of parameters to your BoundStatement using boundStatement.setXXXX(index,value) as follows :
BoundStatement statement = new BoundStatement(query);
statement.setString(0, "value");
statement.setInt(1, 1);
statement.setDate(2, new Date());
ResultSet results = session.execute(statement);
The problem though is that you're trying to use a dynamic column family whose value changes with the value you want to bind.
As far as I know, this is not allowed so you should instead prepare one statement per table and then use the right bound statement.
Is there an easy way to check if table (column family) is defined in Cassandra using CQL (or API perhaps, using com.datastax.driver)?
Right now I am leaning towards executing SELECT 1 FROM table and checking for exception but maybe there is a better way?
As of 1.1 you should be able to query the system keyspace, schema_columnfamilies column family. If you know which keyspace you want to check, this CQL should list all column families in a keyspace:
SELECT columnfamily_name
FROM schema_columnfamilies WHERE keyspace_name='myKeyspaceName';
The report describing this functionality is here: https://issues.apache.org/jira/browse/CASSANDRA-2477
Although, they do note that some of the system column names have changed between 1.1 and 1.2. So you might have to mess around with it a little to get your desired results.
Edit 20160523 - Cassandra 3.x Update:
Note that for Cassandra 3.0 and up, you'll need to make a few adjustments to the above query:
SELECT table_name
FROM system_schema.tables WHERE keyspace_name='myKeyspaceName';
The Java driver (since you mentioned it in your question) also maintains a local representation of the schema.
Driver 3.x and below:
KeyspaceMetadata ks = cluster.getMetadata().getKeyspace("myKeyspace");
TableMetadata table = ks.getTable("myTable");
boolean tableExists = (table != null);
Driver 4.x and above:
Metadata metadata = session.getMetadata();
boolean tableExists =
metadata.getKeyspace("myKeyspace")
.flatMap(ks -> ks.getTable("myTable"))
.isPresent();
I just needed to manually check for the existence of a table using cqlsh.
Possibly useful general info.
describe keyspace_name.table_name
If it doesn't exist you'll get 'table_name' not found in keyspace 'keyspace'
If it does exist you'll get a description of the table.
For the .NET driver CassandraCSharpDriver version 3.17.1 the following code creates a table if it doesn't exist yet:
var ks = _cassandraSession.Cluster.Metadata.GetKeyspace(keyspaceName);
var tableNames = ks.GetTablesNames();
if(!tableNames.Contains(tableName.ToLowerInvariant()))
{
var stmt = new SimpleStatement($"CREATE TABLE {tableName} (id text PRIMARY KEY, name text, price decimal, volume int, time timestamp)");
_cassandraSession.Execute(stmt);
}
You will need to adapt the list of table columns to your needs. This can also be awaited by using await _cassandraSession.ExecuteAsync(stmt).ConfigureAwait(false) in an async method.
Also, I want to mention that I'm using Cassandra version 4.0.1.
trying to write a query which will paginate through all rows in a column family using astyanax client and RowSliceQuery.
keyspace.prepareQuery(COLUMN_FAMILY).getKeyRange(null, null, null, null, 100);
Done this successfully using hector where 1st call is done with null start and end keys. After retrieving 1st page I use last key from the result to make query for second page and etc. This is code for 1st page using hector.
HFactory.createRangeSlicesQuery(keyspace,
LongSerializer.get(), new CompositeSerializer(),
BytesArraySerializer.get())
.setColumnFamily(COLUMN_FAMILY)
.setRange(null, null, false, 100).setRowCount(100);
Now when I am trying to do this with astyanax I am getting errors about null and non-null keys and tokens. Not sure what tokens do in this query. Also I am able to use allRows(), but would like to do this using key range query as it gives me more flexibility.
Does anybody have an example of key range query using astyanax? I cannot find an example neither in "getting started" documentation or anywhere else on the net.
Thanks!
Anton
What you are referring to is the getRowRange method:
keyspace.prepareQuery(CF_STANDARD1)
.getRowRange(startKey, endKey, startToken, endToken, count)
Note however that this works only when the ByteOrderedPartitioner is used. Since by default Cassandra uses the Murmur3Partitioner, this will usually not work. Using an index to do this instead is recommended. Astyanax also provides the reverse index search recipe which takes advantage of a second column family which stores your keys as columns to allow efficient range searches on the original data.
Check this sample code. I hope this code will help you in doing the paging.
IndexQuery<String, String> query = keyspace
.prepareQuery(CF_STANDARD1).searchWithIndex()
.setRowLimit(10).autoPaginateRows(true).addExpression()
.whereColumn("Index2").equals().value(42);
Best,