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Indexing a simple Java Record

I have a Java Object, Record . It represents a single record as a result of SQL execution. Can CQEngine index collection of Record ?
My class is of the form
public class Record {
private List<String> columnNames;
private List<Object> values;
... Other getters
}
I have looked through some examples, but I have no luck there.
I want to index only specific column(s) with its name and corresponding value. Can this be achived using cqengine or is there any other alternatives to achieve the same.
Thanks.

That seems to be a strange way to model data, but you can use CQEngine with that model if you wish.
(First off, CQEngine will have no use for your column names so you can remove that field.)
To do this, you will need to define a CQEngine virtual attribute for each of the indexes in your list of values.
Each attribute will need to be declared with the data type which will be stored in that column/index, and will need to be able to cast the object at that index in your list of values, to the appropriate data type (String, Double, Integer etc.).
So let's say your Record has a column called 'price', which is of type Double, and is stored at index 5 in the list of values. You could define an attribute which reads it as follows:
public static final Attribute<Record, Double> PRICE =
attribute("PRICE", record -> ((Double) record.values.get(5));
If this sounds complicated, it's because that way of modelling data makes things a bit complicated :) It's usually easier to work with a data model which leverages the Java type system (which your model does not). As such, you will need to keep track of the data types etc. of each field programmatically yourself.
CQEngine itself will work fine with that model though, because at the end of the day CQEngine attributes don't need to read fields, the attributes are just functions which are programmed to fetch values.
There's a bunch of stuff not covered above. For example can your values be null? (if so, you should use the nullable variety of attributes as discussed in the CQEngine docs. Or, might each of your Record objects have different sets of columns? (if so, you can create attributes on-the-fly when you encounter a new column, but you should probably cache the attributes you have created somewhere).
Hope that helps,
Niall (CQEngine author)

How to retrieve only part (few) of pojo fields in Hibernate?

I have a situation where I need to return only few fields of a POJO.
Here is a SOF Question: retrieve-single-field-rather-than-whole-pojo-in-hibernate question regarding the same, but few things still seems to be obscure.
1) The answer suggests to use -
String employeeName = session.createQuery("select empMaster.name from EmployeeMaster empMaster where empMaster.id = :id").setInteger("id",10).uniqueResult();
So, here is my concern - Every pojo field is normally private, so "empMaster.name" will simply not work. And am not sure if empMaster.getName() is the solution for this. Will calling the getter methods work?
2) If i am querying multiple fields, (which is my case) (assuming getter methods work) the query will be some thing like -
List<String> employeeDetails = session.createQuery("select empMaster.getName(), empMaster.getDesignation() from EmployeeMaster empMaster where empMaster.id = :id").setInteger("id",10).uniqueResult();
Note the return type has changed from String to List<String>.
2(a) Hope this is right?
2(b) what if i am interested in age/salary of employee which will be of int type. I think the return type will be List<String> or List<Object>. Well any how in the application i can recast the String or Object to the proper type int or float etc. So this should not be a problem.
3) Now what if I am querying multiple employee details (no where clause), so the query will be something like - (not sure if the part of query after from is correct)
List<List<<String>> employeesDetails = session.createQuery("select empMaster.getName(), empMaster.getDesignation() from EmployeeMaster;
Anyway, point here is to emphasise the change in the return type to : List<List<<String>> employeesDetails. Does it work this way ???.
(The question quoted above also has answers pointing to use Projections. I have questions about it but will post them on another question, don't want to mixup.)

I will list the points in the order you mentioned them:
The query has nothing to do with the POJO's field visibility. You are doing a simple query to the database, as if you were doing a query using SQL, and columns in a table have nothing to do with the fact that their mapped POJOs' fields in an application are public or private. The difference is only the language that you're using: now you're using the Hibernate Query Language (HQL), which allows you to express your query with respect to the POJOs' definitions instead of the database's tables' definitions. In fact, doing
session.createQuery("select empMaster.getName() from EmployeeMaster...");
will throw a syntax error: there can be no parenthesis in an object's field name.
By the way, you have to parse your query result to a String, otherwise there would be a compiler semantics error.
String name = (String) session.createQuery("select empMaster.name from EmployeeMaster...").setYourParameters().uniqueResult();
When you do a query whose SELECT clause contains more than one field, and you call uniqueResult(), you're obtaining an array of Objects (Object[]). You iterate through each element in the array and cast it to the corresponding type.
First of all, you probably forgot to add a .list() method call at the end of your query.
session.createQuery("select empMaster.name, empMaster.designation from EmployeeMaster").list();
Otherwise, the query will not be executed, and you would just have a QueryImpl object waiting to be triggered.
Now, when you're expecting multiple results in your query and selecting several fields, you're getting back a List<Object[]>. The elements of the list will be the array of fields for a specific record, and the array per se will be the fields.

Building an Array from an ResultSet?

I'm pretty new to the whole SQL and Java thing, but here I'm actually really confused.
I have a method which is called by invoking a few array parameters, as following
Method(String[], int, int[], int[])
I'm doing a ResultSet to check to see if there are any rows available where there is an ID match for the searched item.
ResultSet group = statement.executeQuery("SELECT * FROM `circulation` WHERE `ItemID` = "+itemID);
However, I'm completely stumped here on how to construct the method.
The String[], and int[] parameters are what is stored in the database, while the standard int parameter is the itemID. I have no idea how to go about doing this to call the Method correctly.
Darn, I thought I was doing good, too.

Arguments are normally used to provide information to the method being called. To get information from the method being called, you normally use a return value.
Your method seems to search rows in a database table named circulation for a given item ID. The item ID should thus be an argument. The found rows should be a returned value. The signature of the method should thus be:
Circulation[] findByItemId(int itemId);
Or better, using collections instead of arrays:
List<Circulation> findByItemId(int itemId);
What is Circulation? It's a class that represents what a row of the circulation table contains. So if the table contains an ID, a name and an item ID, this class would look like
public class Circulation {
private int id;
private String name;
private int itemId;
// constructor, getters, and other useful methods omitted for brevity
}
Your findByItemId() method will thus create an empty list of Circulation, then iterate over the rows of the result set, construct a Circulation instance for each row, and add the instance to the list. And then it will return that list.
Finally, you're using concatenation to build a SQL query taking parameters. This is dangerous. You should use a prepared statement instead. Read the tutorial about them.

Take a look at Apache commons-dbutils. It is a simple wrapper around JDBC and lets you convert your resultsets into any standard datastructures

You can use function
rs.getArray()
with columnName or ColumnLabel.
But this function return objects array and you can cast it to Integer and String.

Storing various object types in single column of database

I am working in Java. I have an class called Command. This object class stores a variable List of parameters that are primitives (mostly int and double). The type, number, and order of parameters is specific to each command, so the List is type Object. I won't ever query the table based on what these parameter values are so I figured I would concatenate them into a single String or serialize them in some way. I think this may be a better approach that normalizing the table because I will have to join every time and that table will grow huge pretty quickly. (Edit: The Command object also stores some other members that won't be serialized such as a String to identify the type of command, and a Timestamp for when it was issued.)
So I have 2 questions:
Should I turn them into a delimited String? If so, how do I get each object as a String without knowing which type to cast them to? I attempted to loop through and use the .toString method, but that is not working. It seems to be returning null.
Or is there some way to just serialize that data of the array into a column of the DB? I read about serialization and it seems to be for the context of serializing whole classes.

I would use JSON serializer and deserializer like Jackson to store and retrieve those command objects in DB without losing the specific type information. On a side note, I would have these commands implement a common interface and store them in a list of commands and not in a list of objects.

PlayFramework get field from model select

Since the play documentation on models is terrible I'll ask here. I have the basic code;
public static void Controller() {
List<Item> item = Item.find("SELECT itemname,id FROM Item WHERE itembool = true ORDER BY itemcreated ASC LIMIT 0,1").fetch();
if ( item == null ) {
notFound();
}
}
What I'm trying to do is get the value for 'itemname' returned for the first value returned from an SQL query (The real query is much more complicated and other things so it can't be replaced with methods). I can get the entire first object with item.get(0) but I can't figure out how to get the value of 'itemname' as a string and it doesn't seem to be documented anywhere.
Edit
Probably should have mentioned in the original question, I need to retrieve by field name, not index. I.E. I can't do items.get(0)[0]; I need to do items.get(0)['itemname'];

The documentation explains this if you read it, in here. Hibernate doesn't use SQL, but JPQL, which has a different syntax as it works with objects, not individual fields.
What you want to do can be achieved in two ways (both in the documentation):
List<Item> item = Item.find("SELECT i FROM Item i WHERE i.itembool = true ORDER BY i.itemcreated ASC").fetch(1);
List<Item> item = Item.find("itembool = true ORDER BY itemcreated ASC").fetch(1);
EDIT:
On the retrieval part, you will get a list of Item, so you can just access the field directly on the object:
item.get(0).getItemName();

Since Play uses Hibernate under the hood, you need to take a look at Hibernate's documentation.
In particular, SELECT itemname,id ... yields Object[] rather than Item, so that you can get itemname as follows:
List<Object[]> items = ...;
String itemname = items.get(0)[0];

well if you have to do a select itemname,id ..., you would not be able to do a items.get(0)["itemname"] because as axtavt and Pere have mentioned, you would get a Object[] back. You can instead create another (perhaps immutable) entity class that can be used in this query. Please refer to hibernate documentation for details. You can then model the entity based on your query requirements and use it to fetch information, thus letting hibernate handle all the magic number game for you. That ways, you would have a bean with filled up values that you can use to map back to your model class if you like.
HTH!