We Keep Coding

How to use Sum SQL with Spring Data MongoDB?

I want to sum the values of a column price.value where the column validatedAt is between startDate and endDate.
So I want a BigInteger as a result (the sum value).
This is what I tried:
final List<AggregationOperation> aggregationOperations = new ArrayList<>();
aggregationOperations.add(Aggregation.match(where("validatedAt").gte(startDate).lt(endDate)));
aggregationOperations.add(Aggregation.group().sum("price.value").as("total"));
final Aggregation turnoverAggregation = Aggregation.newAggregation(OrderEntity.class, aggregationOperations);
return this.mongoOperations.aggregate(turnoverAggregation, OrderEntity.class, BigInteger.class).getUniqueMappedResult();
This doesn't work. I have this error:
{"exception":"com.application.CommonClient$Builder$6","path":"/api/stats/dashboard","message":"Failed to instantiate java.math.BigInteger using constructor NO_CONSTRUCTOR with arguments ","error":"Internal Server Error","timestamp":1493209463953,"status":500}
Any help?

You don`t need to add a new pojo for just for this. It is helpful when you more fields to map and you want spring to map them automatically.
The correct way to fix the problem is to use BasicDBObject because MongoDB stores all values as key value pairs.
return this.mongoOperations.aggregate(turnoverAggregation, OrderEntity.class, BasicDBObject.class).getUniqueMappedResult().getInt("total");
Sidenote: You should use Double/BigDecimal for monetary values.

I resolved this problem by creating a class that has a BigInteger attribute:
private class Total {
private int total;
}
return this.mongoOperations.aggregate(turnoverAggregation, OrderEntity.class, Total.class).getUniqueMappedResult();

Get key from HashMap in Android by position or index

I have:
public static HashMap<String, String> CHILD_NAME_DOB = new HashMap<>();
Suppose the values in CHILD_NAME_DOB are:
<adam,15121990>
<roy,01051995>
<neha,05091992>
<alisha,11051992>
I am trying to fetch the last key element from CHILD_NAME_DOB. That is, I want to fetch key alisha from the example above to temporary String name.
Also I want to know on how to fetch data by index.
Eg.: if int index = 2 , I want key "Neha" in String name
TIA.
Edit: DateOfBirth value (value data in CHILD_NAME_DOB) is dynamic and is unknown. So THIS LINK is not what I want.

Single line solution:
First note that the Java HashMap does not guarantee the order of entries. So each time you iterate over a HashMap, entries appear in different positions. You will need LinkedHashMap that guarantees the predictable iteration order.
Map<String, String> CHILD_NAME_DOB = new LinkedHashMap<>();
Get the key by index:
key = (new ArrayList<>(CHILD_NAME_DOB.keySet())).get(index)
Get the value by index:
CHILD_NAME_DOB.get(key)

Thanks to #Pentium10 for this answer.
And I little modified it according to my need.
String key="default";
Iterator myVeryOwnIterator = CHILD_NAME_DOB.keySet().iterator();
while(myVeryOwnIterator.hasNext()) {
key=(String)myVeryOwnIterator.next();
//String value=(String)meMap.get(key);
}
Toast.makeText(viewEnterChildExp.getContext(), "Key: "+key , Toast.LENGTH_LONG).show();
I'm getting the last key element by this.
I'll update as soon I also get to find an easy way to key by index.

This way to get key....
public static String getHashMapKeyFromIndex(HashMap hashMap, int index){
String key = null;
HashMap <String,Object> hs = hashMap;
int pos=0;
for(Map.Entry<String, Object> entry : hs.entrySet())
{
if(index==pos){
key=entry.getKey();
}
pos++;
}
return key;
}

You can also use an ArrayMap instead of a HashMap. To get the value by index use:
ArrayMap.valueAt(index);
To get the Key at an index use:
ArrayMap.keyAt(index);

Fetching the "last" key and fetch by index is not supported by HashMap. You can use a LinkedHashMap and lookup the element with index 2 (or the last element) by iterating over it. But this will be a O(n) operation.
I suggest you use a List<Pair<String, String>> if the order of the keys/values is important to you and you wish to do index based lookup.
If both key based and index based lookup is important to you, you could use a combined data structure that consists of both a List and a HashMap, but note that removal of elements will be O(n).

You can create a class Child
public class Child(){
private String name;
private String number;
....
}
and then put this object in a List
public static List<Child> CHILD_NAME_DOB = new ArrayList<Child>(); // using LinkedList would defeat the purpose
in this way you can invoke the method get(int index), that returns the element at the specified position in this list.
In your example
<adam,15121990>
<roy,01051995>
<neha,05091992>
<alisha,11051992>
invoking CHILD_NAME_DOB.get(2) you'll get <neha,05091992>(as Child object)

HashMap does not have a concept of ordering, so getting the n-th entry does not make sense. You could use a TreeMap instead, which is ordered on its keys.
However, you should reconsider your model as you seem to have conflicting interests. On the one hand, accessing by index is typical for Lists, whereas accessing by key is typical for Maps. I'm not sure in which situation you'd want to do both.
If you really want to do both index and key accessing, you could write your own data structure that stores the data in a list combined with a mapping from key to index and vice versa. I would recommend against this, but if that's really what you want, then I think that's the best solution.

I know it is not the best solution, but what about this solution (pseudocode!). Just combine List and Map in one class.
public class UserBirthday {
private List<String> names = new ArrayList<>();
private Map<String, String> CHILD_NAME_DOB = new HashMap<String, String>();
public void add(String name, String bd) {
if (!CHILD_NAME_DOB.containsKey(name)) {
names.add(name);
}
CHILD_NAME_DOB.put(name, bd);
}
public String getByName(String name) {
return CHILD_NAME_DOB.get(name);
}
public String getByIndex(int index) {
return getByName(names.get(index)); // TODO: range test
}
public static void main(String[] args) {
UserBirthday ub = new UserBirthday();
ub.add("dit", "12345678");
ub.add("lea", "234239423");
ub.add("alex", "43534534");
ub.add("ted", "099098790");
System.out.println(ub.getByIndex(2));
System.out.println(ub.getByName("alex"));
}
}
You may get some problems if you remove an entry, but it should be just a suggestion.

for (String key : hmList.keySet()) {
String value = hmList.get(key);
Log.e("HashMap values", "key=" + key + " ,value=" + value);
}

Best way to save some data and then retrieve it

I have a project where I save some data coming from different channels of a Soap Service, for example:
String_Value Long_timestamp Double_value String_value String_value Int_value
I can have many lines (i.e. 200), with different values, like the one above.
I thought that I could use an ArrayList, however data can have a different structure than the one above, so an ArrayList maybe isn't a good solution in order to retrieve data from it.
For example above I have, after the first two values that are always fixed, 4 values, but in another channel I may have 3, or 5, values. What I want retrieve data, I must know how many values have a particular line, and I think that Arraylist doesn't help me.
What solution could I use?

When you have a need to uniquely identify varying length input, a HashMap usually works quite well. For example, you can have a class:
public class Record
{
private HashMap<String, String> values;
public Record()
{
// create your hashmap.
values = new HashMap<String, String>();
}
public String getData(String key)
{
return values.get(key);
}
public void addData(String key, String value)
{
values.put(key, value);
}
}
With this type of structure, you can save as many different values as you want. What I would do is loop through each value passed from Soap and simply add to the Record, then keep a list of Record objects.
Record rec = new Record();
rec.addData("timestamp", timestamp);
rec.addData("Value", value);
rec.addData("Plans for world domination", dominationPlans);

You could build your classes representing the entities and then build a parser ... If it isn't in a standard format (eg JSON, YAML, ecc...) you have no choice to develop your own parser .

Create a class with fields.
class ClassName{
int numberOfValues;
String dataString;
...
}
Now create an ArrayList of that class like ArrayList<ClassName> and for each record fill that class object with numberOfValues and dataString and add in Arraylist.

Retrieving timestamp from hbase row

Using Hbase API (Get/Put) or HBQL API, is it possible to retrieve timestamp of a particular column?

Assuming your client is configured and you have a table setup. Doing a get returns a Result
Get get = new Get(Bytes.toBytes("row_key"));
Result result_foo = table.get(get);
A Result is backed by a KeyValue. KeyValues contain the timestamps. You can get either a list of KeyValues with list() or get an array with raw(). A KeyValue has a get timestamp method.
result_foo.raw()[0].getTimestamp()

I think the follow will be better:
KeyValue kv = result.getColumnLatest(family, qualifier);
String status = Bytes.toString(kv.getValue());
Long timestamp = kv.getTimestamp();
since Result#getValue(family, qualifier) is implemented as
public byte[] getValue(byte[] family, byte[] qualifier) {
KeyValue kv = this.getColumnLatest(family, qualifier);
return kv == null ? null : kv.getValue();
}

#codingFoo's answer assumes all timestamps are the same for all cells, but op's question was for a specific column. In that respect, similar to #peibin wang's answer, I would propose the following if you would like the last timestamp for your column:
Use the getColumnLatestCell method on your Result object, and then call the getTimestamp method like so:
Result res = ...
res.getColumnLatestCell(Bytes.toBytes("column_family"), Bytes.toBytes("column_qualifier")).getTimestamp();
If you want access to a specific timestamp you could use the getColumnCells which returns all cells for a specified column, but then you will have to choose between the cells with a get(int index) and then call getTimestamp()

result_foo.rawCells()(0).getTimestamp
is a good style

How to check if a Set contains an object which has one member variable equal to some value

I have a java Set of Result objects. My Result class definition looks like this:
private String url;
private String title;
private Set<String> keywords;
I have stored my information in a database table called Keywords which looks like this
Keywords = [id, url, title, keyword, date-time]
As you can see there isn't a one-to-one mapping between an object and a row in the database. I am using SQL (MySQL DB) to extract the values and have a suitable ResultSet object.
How do I check whether the Set already contains a Result with a given URL.
If the set already contains a Result object with the current URL I simply want to add the extra keyword to the Set of keywords, otherwise I create a new Result object for adding to the Set of Result objects.

When you iterate over the JDBC resultSet (to create your own set of Results) why don't you put them into a Map? To create the Map after the fact:
Map<String, List<Result>> map = new HashMap<String, List<Result>>();
for (Result r : resultSet) {
if (map.containsKey(r.url)) {
map.get(r.url).add(r);
} else {
List<Result> list = new ArrayList<Result>();
list.add(r);
map.put(r.url, list);
}
}
Then just use map.containsKey(url) to check.

Normalization is your friend
http://en.wikipedia.org/wiki/Database_normalization

If it's possible, I suggest changing your database design to eliminate this problem. Your current design requries storing the id, url, title and date-time once per key word, which could waste quite a bit of space if you have lots of key words
I would suggest having two tables. Assuming that the id field is guarenteed to be unique, the first table would store the id, url, title and date-time and would only have one row per id. The second table would store the id and a key word. You would insert multiple rows into this table as required.
Is that possible / does that make sense?

You can use a Map with the URLs as the keys:
Map<String, Result> map = new HashMap<String, Result>();
for (Result r : results) {
if (map.containsKey(r.url)) {
map.get(r.url).keywords.addAll(r.keywords);
} else {
map.put(r.url, r);
}
}

I think that you need to make an override on equals() method of your Result class. In that method you will put your logic that will check what you are looking for.
N.B. You also need to know that overrideng the equals() method, you need to override also hashCode() method.
For more on "overriding equals() and hashCode() methods" topic you can look at the this another question.