I've some collections on my database that have a 'Dynamic Name',
Let's say that I've some collections that store Animals data from an specific country,
So in my database Animals I would have the following collections:
Australia-Animals
Japan-Animals
Brazil-Animals
And from time to time I need to add new collections to my Database, currently I've an Script that add an Index to the country like:
public class CreateIndexForAnimalSpecies {
#ChangeSet(order = "1", id = "CreateIndexForAnimalSpecies", author = "Foo Bar")
public void createIndexForAnimalSpecies(final MongockTemplate template)
IndexOperations idx = mongockTemplate.indexOps("Australia-Animals");
Index index = new Index().named("specieIndex").on("specie", Direction.ASC).background();
idx.ensureIndex(index);
}
Basically this class does the job of creating the index for the Collection named Australia-Animals but in the future if I add a new collection with a new Country Prefix I would have to copy this whole piece of code and change the Collection's name String.
I tried using *, $, %, as Regex but none of them worked. There's any alternative method along fetching the collections name and add to a list with contains("name")?
I tough of something like:
Set<String> collections = mongockTemplate.getCollectionNames();
// Convert to a List<String>
for(String c: collections){
if(c.contains("-Animals"){
otherList.add(c);
}
}
otherList.forEach(item -> scriptToCreateIndex(item));
It works, but seems quite inefficient having to iterate over the collections to do the job.
Related
I have this object
Class A {
int count;
String name;
}
I have a list of my above custom object as below :
List<A> aList = new ArrayList<>();
A a = new A(1,"abc");
A b = new A(0,"def");
A c = new A(0,"xyz");
aList.add(a);
aList.add(b);
aList.add(c);
I will get this list as input in my service. Now based upon some scenario, first I need to set "count" to ZERO for all elements in the list and based on a check with "name" I need to set the count as ONE for a particular name.
This is how I am doing now :
String tempName = "Some Name like abc/def/xyz";
alist.stream().forEach(x -> x.setCount(0));
aList.stream().filter(x -> x.getName().equalsIgnoreCase(tempName))
.findFirst()
.ifPresent(y -> y.setCount(1));
This is doing my job, but I want to know if I can simplify the above logic and use one single stream instead of two and improve the performance by avoiding looping through the list twice.
Just check if the name matches in the first loop:
alist.forEach(x -> x.setCount(x.getName().equalsIgnoreCase(tempName) ? 1 : 0));
According to a business requirement, I will need not check if the value of an attribute if it equal to a list of given string values.
I am wondering what is the better way to do it, in case if someday there is a new value that needs to be added. Should these values be stored in a table?
List<String> values = new ArrayList<>();
values.add("value1");
values.add("value2");
values.add("value3");
if(values.contains(brand){
// if the brand contains the given values
// implement a specific logic
}
Thank you
You could do it like this. If there was a Brand class that returned an immutable list of attributes.
Brand brand = new Brand(...);
List<String> values = new ArrayList<>();
values.add("value1");
values.add("value2");
values.add("value3");
if(brand.getAtrributes().containsAll(values)) {
// do something.
}
But imo, it would be better to use an EnumSet and define the attributes as enums.
enum Attr {VALUE1, VALUE2, VALUE3,VALUE4, VALUE5};
EnumSet<Attr> attr = EnumSet.of(Attr.VALUE1, Attr.VALUE2, Attr.VALUE3, Attr.VALUE4, Attr.VALUE5);
if(attr.contains(Attr.VALUE1)) {
// do something.
}
There is still a containsAll method as well as other potentially helpful methods.
create a record that takes an set of enums
create an instance of that with values 2-4.
And use the range feature to verify.
record Brand(EnumSet<Attr> getAttributes){}
Brand brand = new Brand(EnumSet.of(Attr.VALUE2,Attr.VALUE3, Attr.VALUE4));
EnumSet<Attr> required = EnumSet.range(Attr.VALUE2,Attr.VALUE4);
if (brand.getAttributes().containsAll(required)) {
System.out.println("Good to go");
}
Prints
Good to go.
I have list of words which I need to load to ArrayList< String >
prefix.properties
vocab\: = http://myweb.in/myvocab#
hydra\: = http://www.w3.org/ns/hydra/core#
schema\: = http://schema.org/
"vocab:" is actually "vocab:" .Slash(\) is used to read colon(:) character because it is special character.
Dictionary.java
public class Dictionary {
public static ArrayList<String> prefix = new ArrayList<>();
static {
Properties properties = new Properties();
InputStream input = null;
input = ClassLoader.getSystemResourceAsStream("prefix.properties");
System.out.println(input!=null);
try {
properties.load(input);
} catch (IOException e) {
e.printStackTrace();
}
Set<Map.Entry<Object, Object>> entries = properties.entrySet();
for(Map.Entry<Object, Object> E : entries)
{
prefix.add(E.getKey().toString());
prefix.add(E.getValue().toString());
}
}
}
In Dictionary.java , ArrayList prefix will have
prefix = [
"vocab:",
"http://myweb.in/myvocab#",
"hydra:",
"http://www.w3.org/ns/hydra/core#",
"schema:",
"http://schema.org/"
]
I am querying some data in another class.
For eg:
public class QueryClass
{
public ArrayList<String> queryResult(String findKey)
{
ArrayList<String> result = new ArrayList<String>();
ArrayList<String> prefix = Dictionary.prefix;
Iterator<String> iterator = prefix.iterator();
while (iterator.hasNext())
{
String currentKey = iterator.next()+findKey;
/**
Here my logic to search data with this currentKey
*/
}
return result;
}
}
Problem :
I want to avoid this method to load from .properties file because there is possibility of odd number of elements can be present while .properties file provide (key,value) pair way to store data.
Reason why I have to load from separate file ? Because In future I will have to add more keywords/String thats why I put it in prefix.properties file.
Is there any alternative way to do this?
Do not re-invent the wheel.
If you can define the file format, then just go for java properties.
You see, the Properties class has a method getProperty(String, String) where the second argument can be used to pass a default value for example. That method could be used in order to fetch keys that don't come with values.
I would be really careful about inventing your own format; instead I would look into ways of re-using what is already there. Writing code is similar to building roads: people forget that each new road that is built translates to maintenance efforts in the future.
Besides: you add string values to a list of strings by calling list.add(strValue). That is all that is to that.
Edit on your comment: when "java properties" are not what you are looking for; then consider using other formats. For example you could be persisting your data in some JSON based format. And then just go for some existing JSON parser. Actually, your data almost looks like JSON already.
I'm not sure why you need to use ArrayList but if you want to pass these property keys/values, there are 2 better ways:
Use Properties itself.
Convert to HashMap.
First some background about my Problem:
I am building a crawler and I want to monitor some highscore lists.
The highscore lists are defined by two parameters: a category and a collection (together unique).
After a successful download I create a new stats entry (category, collection, createdAt, ...)
Problem: I want to query the highscore list only once per day. So I need a query that will return category and collection that haven't been downloaded in 24h.
The stats Table should be used for this.
I have a List of all possible categories and of all possible collections. They work like a cross join.
So basically i need the relative complement of the cross join with the entries from the last 24h
My Idea: Cross join categories and collections and 'substract' all Pair(category, collection) of stats entries that has been created during last 24 h
Question 1: Is it possible to define categories and collections inside the query and cross join them or do I have to create a table for them?
Question 2: Is my Idea the correct approach? How would you do this in Sqlite?
Ok i realise that this might sound confusing so I drew an image of what I actually want.
I am interested in C.
Here is my current code in java, maybe it helps to understand the problem:
public List<Pair<String, String>> getCollectionsToDownload() throws SQLException {
long threshold = System.currentTimeMillis() - DAY;
QueryBuilder<TopAppStatistics, Long> query = queryBuilder();
List<TopAppStatistics> collectionsNotToQuery = query.where().ge(TopAppStatistics.CREATED_AT, threshold).query();
List<Pair<String, String>> toDownload = crossJoin();
for (TopAppStatistics stat : collectionsNotToQuery) {
toDownload.remove(new Pair<>(stat.getCategory(), stat.getCollection()));
}
return toDownload;
}
private List<Pair<String, String>> crossJoin() {
String[] categories = PlayUrls.CATEGORIES;
String[] collections = PlayUrls.COLLECTIONS;
List<Pair<String, String>> toDownload = new ArrayList<>();
for (String ca : categories) {
for (String co : collections) {
toDownload.add(new Pair<>(ca, co));
}
}
return toDownload;
}
The easiest solution to your problem is an EXCEPT. Say you have a subquery
that computes A and another one that computes B. These queries
can be very complex. The key is that both should return the same number of columns and comparable data types.
In SQLite you can then do:
<your subquery 1> EXCEPT <your subquery 2>
As simple as that.
For example:
SELECT a, b FROM T where a > 10
EXCEPT
SELECT a,b FROM T where b < 5;
Remember, both subqueries must return the same number of columns.
Edit: My list is sorted as it is coming from a DB
I have an ArrayList that has objects of class People. People has two properties: ssn and terminationReason. So my list looks like this
ArrayList:
ssn TerminatinoReason
123456789 Reason1
123456789 Reason2
123456789 Reason3
568956899 Reason2
000000001 Reason3
000000001 Reason2
I want to change this list up so that there are no duplicates and termination reasons are seperated by commas.
so above list would become
New ArrayList:
ssn TerminatinoReason
123456789 Reason1, Reason2, Reason3
568956899 Reason2
000000001 Reason3, Reason2
I have something going where I am looping through the original list and matching ssn's but it does not seem to work.
Can someone help?
Code I was using was:
String ssn = "";
Iterator it = results.iterator();
ArrayList newList = new ArrayList();
People ob;
while (it.hasNext())
{
ob = (People) it.next();
if (ssn.equalsIgnoreCase(""))
{
newList.add(ob);
ssn = ob.getSSN();
}
else if (ssn.equalsIgnoreCase(ob.getSSN()))
{
//should I get last object from new list and append this termination reason?
ob.getTerminationReason()
}
}
To me, this seems like a good case to use a Multimap, which would allow storing multiple values for a single key.
The Google Collections has a Multimap implementation.
This may mean that the Person object's ssn and terminationReason fields may have to be taken out to be a key and value, respectively. (And those fields will be assumed to be String.)
Basically, it can be used as follows:
Multimap<String, String> m = HashMultimap.create();
// In reality, the following would probably be iterating over the
// Person objects returned from the database, and calling the
// getSSN and getTerminationReasons methods.
m.put("0000001", "Reason1");
m.put("0000001", "Reason2");
m.put("0000001", "Reason3");
m.put("0000002", "Reason1");
m.put("0000002", "Reason2");
m.put("0000002", "Reason3");
for (String ssn : m.keySet())
{
// For each SSN, the termination reasons can be retrieved.
Collection<String> termReasonsList = m.get(ssn);
// Do something with the list of reasons.
}
If necessary, a comma-separated list of a Collection can be produced:
StringBuilder sb = new StringBuilder();
for (String reason : termReasonsList)
{
sb.append(reason);
sb.append(", ");
}
sb.delete(sb.length() - 2, sb.length());
String commaSepList = sb.toString();
This could once again be set to the terminationReason field.
An alternative, as Jonik mentioned in the comments, is to use the StringUtils.join method from Apache Commons Lang could be used to create a comma-separated list.
It should also be noted that the Multimap doesn't specify whether an implementation should or should not allow duplicate key/value pairs, so one should look at which type of Multimap to use.
In this example, the HashMultimap is a good choice, as it does not allow duplicate key/value pairs. This would automatically eliminate any duplicate reasons given for one specific person.
What you might need is a Hash. HashMap maybe usable.
Override equals() and hashCode() inside your People Class.
Make hashCode return the people (person) SSN. This way you will have all People objects with the same SSN in the same "bucket".
Keep in mind that the Map interface implementation classes use key/value pairs for holding your objects so you will have something like myHashMap.add("ssn",peopleobject);
List<People> newlst = new ArrayList<People>();
People last = null;
for (People p : listFromDB) {
if (last == null || !last.ssn.equals(p.ssn)) {
last = new People();
last.ssn = p.ssn;
last.terminationReason = "";
newlst.add(last);
}
if (last.terminationReason.length() > 0) {
last.terminationReason += ", ";
}
last.terminationReason += p.terminationReason;
}
And you get the aggregated list in newlst.
Update: If you are using MySQL, you can use the GROUP_CONCAT function to extract data in your required format. I don't know whether other DB engines have similar function or not.
Update 2: Removed the unnecessary sorting.
Two possible problems:
This won't work if your list isn't sorted
You aren't doing anything with ob.getTerminationReason(). I think you mean to add it to the previous object.
EDIT: Now that i see you´ve edited your question.
As your list is sorted, (by ssn I presume)
Integer currentSSN = null;
List<People> peoplelist = getSortedList();//gets sorted list from DB.
/*Uses foreach construct instead of iterators*/
for (People person:peopleList){
if (currentSSN != null && people.getSSN().equals(currentSSN)){
//same person
system.out.print(person.getReason()+" ");//writes termination reason
}
else{//person has changed. New row.
currentSSN = person.getSSN();
system.out.println(" ");//new row.
system.out.print(person.getSSN()+ " ");//writes row header.
}
}
If you don´t want to display the contents of your list, you could use it to create a MAP and then use it as shown below.
If your list is not sorted
Maybe you should try a different approach, using a Map. Here, ssn would be the key of the map, and values could be a list of People
Map<Integer,List<People>> mymap = getMap();//loads a Map from input data.
for(Integer ssn:mymap.keyset()){
dorow(ssn,mymap.get(ssn));
}
public void dorow(Integer ssn, List<People> reasons){
system.out.print(ssn+" ");
for (People people:reasons){
system.out.print(people.getTerminationReason()+" ");
}
system.out.println("-----");//row separator.
Last but not least, you should override your hashCode() and equals() method on People class.
for example
public void int hashcode(){
return 3*this.reason.hascode();
}