In my Java code I have an object Person with the following properties:
class Person{
int id;
List<Integer> values;
}
I wrote the following query to get the sum and average of each value of a person.
GridCacheQuery<Map.Entry<GridCacheAffinityKey<Integer>, Person>> qry=cache.queries().createSqlQuery(Person.class,"values.get(1) > ? and values.get(2) <= ?");
Iterable<Entry<GridCacheAffinityKey<Long>, Subscriber>> cols = qry.execute(1,10).get();
I know this is not the correct way to query, but I'm not able to identify the correct way to do it.
I'm getting the following errors:
Caused by: org.h2.jdbc.JdbcSQLException: Syntax error in SQL statement "SELECT ""partitioned"".PERSON._KEY,""partitioned"".PERSON._VAL FROM ""partitioned"".PERSON WHERE VALUES.GET([*]1) > ? AND VALUES.GET(2) <= ? ";
SQL statement: SELECT "partitioned".Person._key, "partitioned".Person._val FROM "partitioned".Person WHERE values.get(1) > ? and values.get(2) <= ? [42000-175]
GridGain does not support code snippets embedded into SQL queries. If you want to access these particular elements of your list in query, you can create accessor methods (aliases) for these elements like this:
#GridCacheQuerySqlField
public int first() {
return values.get(1);
}
#GridCacheQuerySqlField
public int second() {
return values.get(2);
}
and use them directly in your query: first > ? and second <= ?
I think predicates can serve your purpopse as well, but not sure if it is faster or slower than the way suggested by
Alexey.
Related
Assume I have the following as the value in an IMap:
public class Employee{
public int empId;
public List<String> categories;
public List<String> getCategories(){
return this.categories;
}
}
I would like to find all employees that belong to category "Sales". Also, I would like to create an index on getCategories() so that the query returns fast. There seems to be no Predicate available to do this. How do I go about achieving this? It seems like I will have to write a Predicate to do this. Is there example code I can look at that would show me how to build a predicate that uses an index ?
The only way I currently see this happening is to denormalize the data model and use something like a IMap and the following as value:
class EmployeeCategory{int employeeId, String category}
And put an index on category.
It is somewhere on the backlog to provide more advances indices that should be able to do this out of the box.
I tried by iterating the List to a separate Imap and then querying it in the client.
IMap<String,ArrayList< categories >> cache=hazelcastInstance.getMap("cache");
IMap<String, categories> cachemodified = hazelcastInstance.getMap("cachemodified") ;
int[] idx = { 0 };
xref.get("urkey").forEach(cachefelement ->{
cachemodified.put(String.valueOf(idx[0]++),cachefelement);
});
Predicate p = Predicates.equal("categoryId", "SearchValue");
Collection<categories> result = cachemodified.values(p);
After reading "Asynchronous queries with the Java driver" article in the datastax blog, I was trying to implement a solution similar to the one in the section called - 'Case study: multi-partition query, a.k.a. “client-side SELECT...IN“'.
I currently have code that looks something like this:
public Future<List<ResultSet>> executeMultipleAsync(final BoundStatement statement, final Object... partitionKeys) {
List<Future<ResultSet>> futures = Lists.newArrayListWithExpectedSize(partitionKeys.length);
for (Object partitionKey : partitionKeys) {
Statement bs = statement.bind(partitionKey);
futures.add(executeWithRetry(bs));
}
return Futures.successfulAsList(futures);
}
But, I'd like to improve on that. In the cql query this BoundStatement holds, I'd like to have something that looks like this:
SELECT * FROM <column_family_name> WHERE <param1> = :p1_name AND param2 = :p2_name AND <partiotion_key_name> = ?;
I'd like the clients of this method to give me a BoundStatement with an already bound parameters (two parameters in this case) and a list of partition keys. In this case, all I need to do, is bind the partition keys and execute the queries. Unfortunately, when I bind the key to this statement I fail with an error - com.datastax.driver.core.exceptions.InvalidTypeException: Invalid type for value 0 of CQL type varchar, expecting class java.lang.String but class java.lang.Long provided. The problem is, that I try to bind the key to the first parameter and not the last. Which is a string and not a long.
I can solve this by either giving the partition parameter a name but then I'd have to get the name via method parameters, or by specifying it's index which again will require an additional method parameter. Either way, if I use the name or the index I have to bind it with a specific type. For instance: bs.setLong("<key_name>", partitionKey);. For some reason, I can't leave it to the BoundStatement to interpret the type of the last parameter.
I'd like to avoid passing the parameter name explicitly and bypass the type problem. Is there anything that can be done?
Thanks!
I've posted the same question in 'DataStax Java Driver for Apache Cassandra User Mailing List' and got an answer saying the functionality that I'm missing may be added in the next version (2.2) of the datastax java driver.
In JAVA-721 (to be introduced in 2.2) we are tentatively planning on
adding the following methods with the signature to BoundStatement:
public BoundStatement setObject(int i, V v) public
BoundStatement setObject(String name, V v)
and
You can emulate setObject in 2.1:
void setObject(BoundStatement bs, int position, Object object,
ProtocolVersion protocolVersion) {
DataType type = bs.preparedStatement().getVariables().getType(position);
ByteBuffer buffer = type.serialize(object, protocolVersion);
bs.setBytesUnsafe(position, buffer);
}
To avoid passing the parameter name, one thing you could do is look
for a position that isn't bound yet:
int findUnsetPosition(BoundStatement bs) {
int size = bs.preparedStatement().getVariables().size();
for (int i = 0; i < size; i++)
if (!bs.isSet(i))
return i;
throw new IllegalArgumentException("found no unset position");
}
I don't recommend it though, because it's ugly and unpredictable if
the user forgot to bind one of the non-PK variables.
The way I would do it is require the user to pass a callback that sets
the PK:
interface PKBinder<T> {
void bind(BoundStatement bs, T pk);
}
public <T> Future<List<ResultSet>> executeMultipleAsync(final BoundStatement statement, PKBinder<T> pkBinder, final T...
partitionKeys)
As a bonus, this will also work with composite partition keys.
I have a cache that looks like this:
Key: UUID
Value: Array[Long]
I want to get the key corresponding to a specific value. How does the where-part look like?
I have tried "value = ?" and "_value = ?" but these obviously doesnt work.
Yo!
What do you mean by Array[Long]? Is it just long[] or may be you are using Scala?
The simplest (but not the most effective) way would be using a scan query with predicate (docs here).
To achieve the best performance it is preferable to have your value indexed, so I'd recommend to have a special wrapper class for your array like this:
class MyArray implements Comparable<MyArray>, Serializable {
private long[] arr;
// implement compareTo,hashCode,equals
#GridCacheQuerySqlField(index = true)
public MyArray indexedArray() {
return this;
}
}
then the query will look like
"indexedArray = ?"
where as parameter you have to pass MyArray instance. It is a bit dirty way to index value but this is the only way right now.
By the way column names for cache key and value in SQL are _key and _val but not _value and you can write queries like
"_val = ? and _key > ?"
of course you have to make sure that your key and value at least implement hashCode and equals correctly, implementing Comparable is preferable.
today I migrated to Astyanax 1.56.42 and discovered, that withValues() on prepared statements doesn't seem to work properly with SQL SELECT...WHERE...IN ().
ArrayList<ByteBuffer> uids = new ArrayList<ByteBuffer>(fileUids.size());
for (int i = 0; i < fileUids.size(); i++) {
uids.add(ByteBuffer.wrap(UUIDtoByteArray(fileUids.get(i)), 0, 16));
}
result = KEYSPACE.prepareQuery(CF_FILESYSTEM)
.withCql("SELECT * from files where file_uid in (?);")
.asPreparedStatement()
.withValues(uids)
.execute();
If my ArrayList contains more than one entry, this results in error
SEVERE: com.netflix.astyanax.connectionpool.exceptions.BadRequestException: BadRequestException: [host=hostname(hostname):9160, latency=5(5), attempts=1]InvalidRequestException(why:there were 1 markers(?) in CQL but 2 bound variables)
What am I doing wrong? Is there any other way to handle a SQL SELECT...WHERE...IN () - statement or did I find a bug?
Best regards
Chris
As you mentioned because you are supplying a collection (ArrayList) to a single ? Astyanax throws an exception. I think you need to add a ? for each element you want to have inside the IN clause.
Say you want to have 2 ints stored in an ArrayList called arrayListObj the where clause, your statement looks like this:
SELECT & FROM users WHERE somevalue IN (arrayListObj);
Because you are suppling a collection, this cant work, so you will need multiple ?'s. I.e. you want :
SELECT name, occupation FROM users WHERE userid IN (arrayListObj.get(0), arrayListObj.get(1));
I couldn't find anything on the Astyanax wiki about using the IN clause with prepared statements.
I have a list AllIDs:
List<IAddress> AllIDs = new List<IAddress>();
I want to do substring operation on a member field AddressId based on a character "_".
I am using below LINQ query but getting compilation error:
AllIDs= AllIDs.Where(s => s.AddressId.Length >= s.AddressId.IndexOf("_"))
.Select(s => s.AddressId.Substring(s.AddressId.IndexOf("_")))
.ToList();
Error:
Cannot implicitly convert type 'System.Collections.Generic.List<string>' to 'System.Collections.Generic.List<MyCompany.Common.Users.IAddress>'
AllIDs is a list of IAddress but you are selecting a string. The compiler is complaining it cannot convert a List<string> to a List<IAddress>. Did you mean the following instead?
var substrings = AllIDs.Where(...).Select(...).ToList();
If you want to put them back into Address objects (assuming you have an Address class in addition to your IAddress interface), you can do something like this (assuming the constructor for Address is in place):
AllIDs = AllIDs.Where(...).Select(new Address(s.AddressID.Substring(s.AddressID.IndexOf("_")))).ToList();
You should also look at using query syntax for LINQ instead of method syntax, it can clean up and improve the readability of a lot of queries like this. Your original (unmodified) query is roughly equivalent to this:
var substrings = from a in AllIDs
let id = a.AddressId
let idx = id.IndexOf("_")
where id.Length >= idx
select id.Substring(idx);
Though this is really just a style thing, and this compiles to the same thing as the original. One slight difference is that you only have to call String.IndexOf() one per entry, instead of twice per entry. let is your friend.
Maybe this?
var boundable =
from s id in AllIDs
where s.AddressId.Length >= s.AddressId.IndexOf("_")
select new { AddressId = s.AddressId.Substring(s.AddressId.IndexOf("_")) };
boundable = boundable.ToList();