Basically, I have a data set where a document can contain an array of variable length. I'm writing a codec, so all I have is BsonReader. The problem is readStartArray() returns void rather than returning, for example, the number of elements. Also, I don't see any methods that allow one to test when the end of the array has been reached (apart from trying readEndArray() and catching the exception).
Any ideas?
I found the documentation for custom serialization to be lacking too, but you just need to work with the Reader.State property. Once you've identified the start of the array you need to iterate over each of the elements until state == BsonReaderState.EndOfArray. You need to ensure that you only call ReadBsonType when the state is "type".
The following example deserializes an array of documents:
context.Reader.ReadStartArray();
bool ctn = true;
do
{
//If in "type" state we can call ReadBsonType. The order is important.
if (context.Reader.State == BsonReaderState.Type)
{
context.Reader.ReadBsonType();
}
//Now that we're in a value state we can read the value safely
if (context.Reader.State == BsonReaderState.Value)
{
if (context.Reader.CurrentBsonType == BsonType.Document)
{
//Handle the document here. In this case pass I it to a private method
DeserializeChild(context, args, node);
}
//state will now be "type", so continue do loop and recheck type
continue;
}
if ( BsonReaderState.EndOfArray == BsonReaderState.EndOfArray)
{
context.Reader.ReadEndArray();
ctn = false;
}
} while (ctn);
Ah, it's done with:
while (reader.readBsonType() == BsonType.DOCUMENT) {
reader.readStartDocument();
// ...
reader.readEndDocument();
}
(it's an array of documents in this case, I'm still new to BSON so I don't know how it would work for an array of values).
Related
I'm learning reactive programming with webflux, and for that I'm migrating some code.
For example I'm trying to migrate this method:
public Set<Vaccine> getAll(Set<Long> vaccinesIds) throws EntityNotFoundException {
if (null == vaccinesIds) {
return null;
}
Set<Long> vaccinesToFind = new HashSet<>(vaccinesIds);
vaccinesToFind.remove(null);
Set<Vaccine> vaccines = new HashSet<>();
vaccineRepository.findByIdIn(vaccinesToFind).forEach(vaccines::add);
if (vaccines.size() != vaccinesToFind.size()) {
LOG.warn("Could not find vaccines with ids: " + vaccinesToFind.removeAll(vaccines.stream().map(Vaccine::getId).collect(Collectors.toSet())));
throw new EntityNotFoundException(VACCINE_ERROR_NOT_FOUND);
}
return vaccines;
}
To summarize the code, if the respository returns all the vaccines that are requested should return the result, if not should return an error.
For that, I thought in something like this, but is not working:
public Flux<Vaccine> getAll(Set<Long> vaccinesIds) {
if (null == vaccinesIds) {
return Flux.empty();
}
Set<Long> vaccinesToFind = new HashSet<>(vaccinesIds);
Flux<Vaccine> byIdIn = vaccineRepository.findByIdIn(vaccinesToFind);
Mono<Long> filter = vaccineRepository.findByIdIn(vaccinesToFind).count().filter(x -> x.equals(Long.valueOf(vaccinesToFind.size())));
return filter.flatMapMany(asd -> vaccineRepository.findByIdIn(vaccinesToFind)
).switchIfEmpty(Flux.error((new EntityNotFoundException(VACCINE_ERROR_NOT_FOUND))));
}
What am I doing wrong?
My first doubt is why the filter is a Mono of Long if it has a equals method in the end. My problem is about evaluating the filter in order to return the list or the error.
First of all, you are querying the same result vaccineRepository.findByIdIn(vaccinesToFind) multiple times. The same data is queried, transferred and deserialized multiple times. This is a sign that something is wrong here.
Let's assume the result set fits into the memory. Then the idea would be to transform flux into a usual collection and to decide whether to emit an error or not:
return vaccineRepository.findByIdIn(vaccinesIds)
.collectList()
.flatMapMany(result -> {
if(result.size() == vaccinesIds.size()) return Flux.fromIterable(result);
else return Flux.error(new EntityNotFoundException(VACCINE_ERROR_NOT_FOUND));
});
In the case the result is to huge for the main memory, you could do count in the db by the first query and in the positive case query the results. The solution is similar to your code:
return vaccineRepository.countByIdIn(vaccinesIds)
.filter(count -> count == vaccinesIds.size())
.flatMapMany($ -> vaccineRepository.findByIdIn(vaccinesIds))
.switchIfEmpty(Mono.error(new EntityNotFoundException(VACCINE_ERROR_NOT_FOUND)));
The result of filter is Mono<Long> because filter just takes the elements from the upstream and tests against the given predicate. If the predicate returns false, the item is filtered out and the Mono is empty. To keep all results of a the test you could use map and the type would be Mono<Boolean>.
I am new to RxJava2.
I am trying to get a list of Transaction object both from cache and from server.
I want to compare the server value to cache value and if the server value is the same, then ignore it.
I was able to do it easily using .scan() because we can return null and when null is returned from the .scan() the value got ignored(filtered).
RxJava 1
private Observable<List<Transaction>> getTransactionsFromCacheAndServer() {
return Observable.concat(
getTransactionsFromCache(),
getTransactionsFromServer()
)
.scan((p1, p2) -> {
if (p1 == null && p2 != null) {
return p2;
} else if (p1 != null && !isListSame(p1, p2)) {
return p2;
} else {
return null;
}
});
}
With RxJava 2, since I cannot return null anymore, things are not easy.
RxJava 2
private Observable<List<Transaction>> getTransactionsFromCacheAndServer() {
return Observable.concat(
getTransactionsFromCache(),
getTransactionsFromServer()
)
.map(FilterObject::new)
.scan((filterObject1, filterObject2) -> {
List<Transaction> p1 = (List<Transaction>)filterObject1.value;
List<Transaction> p2 = (List<Transaction>)filterObject2.value;
if (p1.size() == 0 && p2.size() > 0) {
return filterObject2;
} else if (!isListSame(p1, p2)) {
return filterObject2;
} else {
filterObject2.filter = true;
return filterObject2;
}
})
.filter(filterObject -> !filterObject.filter)
.map(filterObject -> (List<Transaction>)filterObject.value);
}
Where FilterObject is:
public class FilterObject {
public Object value;
public boolean filter;
public FilterObject(Object value) {
this.value = value;
}
}
Even though I can achieve the same thing using above method, it seems very ugly. Also I had to include two maps which might not be so performance friendly.
Is there a simple/clean way to achieve what I want?
I don't think there is a generic solution to this problem, since an empty list and a list that needs to be filtered (which happens to be empty in all cases) are two different things (the output of the scan) and needs to be handled differently.
However, in your particular case you never emit an empty list, except maybe for the first output.
(I am using String instead Transaction, shouldn't matter)
private Observable<List<String>> getTransactionsFromCacheAndServer() {
return Observable.concat(
getTransactionsFromCache(),
getTransactionsFromServer()
)
.filter(list -> !list.isEmpty())
// If you prefer a consistent empty list over the first
// empty list emission getting filtered
.startWith((List<String>) Collections.EMPTY_LIST)
// Newly emitted value cannot be empty, it only depends only on the comparison
.distinctUntilChanged(this::isListSame);
}
That's the closest I could get with as few operators as possible. Hope it solves your problem.
Based on andras' answer, I modified little bit to achieve what I want.
private Observable<List<String>> getTransactionsFromCacheAndServer() {
return Observable.concat(
getTransactionsFromCache(),
getTransactionsFromServer()
)
.filter(list -> !list.isEmpty())
.distinctUntilChanged(this::isListSame)
.switchIfEmpty(Observable.just(new ArrayList<>()));
}
Andreas' answer will always receive an empty list and then a real data.
My solution above will receive:
1. Data from cache (and then data from server if different)
2. Empty list if both cache and server returns Empty list.
I have in a Grid a RealEdit , I set the autodeclaration YES.
The name is myRealEdit , DataSource is myTable and the Field is myRealField.
In the modified method I want to get the value, I need to do a IF control.
IF the value is 0 change the Filed's value IF the value is not 0
throws the value entered and restores the previous value.
I used this code, in modified method:
public boolean modified()
{
boolean ret;
real storedValue;
ret = super();
storedValue = myTable.myRealField; // there is another way to get the value ?
if (myRealEdit.valueStr() == "0")
//accept the value
if (!myRealEdit.valueStr() != "0")
{
myRealEdit.realValue(storedValue);
}
return ret;
}
If the value is not 0 (zero) don't restore the previous value.
I have to use another method ? There is another way to get the real value ?
Thanks in advice,
enjoy!!
Since you are using the modified method in your answer, I suppose you want to put this field validation on the control level (instead of the datasource or table level).
As #Jan B. Kjeldsen suggested in his comment, you should use the validate method to do this validation. Use the modified method only if you want to add some logic that is executed in addition to the field value modification.
The validate method could look similar to
public boolean validate()
{
return this.realValue() == 0 && super() || checkFailed(strFmt("Value %1 is not permitted", this.realValue()));
// TODO please replace this with a Label and explain to the user why the value is not permitted and what he or she can do to resolve this
}
I find a possible way,
I used this code:
public boolean modified()
{
boolean ret;
if (myRealEdit.valueStr() == "0")
{
//accept the value
ret = super();
}
if (!myRealEdit.valueStr() != "0")
{
info("Value not permit");
// nothing to do
}
return ret;
}
In this way, if and only if I have a value 0 I modified the value.
I need to get or read the Real value just inserted from myRealEdit in the modified method.
If the community has comments or improvements inserted, will be more information.
I am trying to look up record using if I have the key then use Find if not use Where
private ApplicationDbContext db = new ApplicationDbContext();
public bool DeactivatePrice(int priceId = 0, string sponsorUserName = "")
{
var prices = db.BeveragePrices;
// if we have an id then find
if (priceId != 0)
{
prices = prices.Find(priceId);
}
else
{
prices = prices.Where(b => b.UserCreated == sponsorUserName);
}
if (prices != null)
{
// do something
}
return true;
I get the following error for
prices = prices.Find(priceId);
Cannot convert app.Model.BeveragePrices from system.data.entity.dbset
I am copying the pattern from this answer but something must be different.
Seems you forgot to put a predicate inside the Find function call. Also you need to do ToList on the collection. The second option is a lot more efficient. The first one gets the whole collection before selection.
Another note commented by #Alla is that the find returns a single element. So I assume another declaration had been made for 'price' in the first option I state down here.
price = prices.ToList.Find(b => b.PriceId == priceId);
Or
prices = prices.Select(b => b.PriceId == priceId);
I assume the field name is PriceId.
//I wrote java code for insertion method on doubly linked list but there is a infinite loop //when I run it. I'm trying to find a bug, but have not found so far. any suggestions?
//it is calling a helper function
public IntList insertionSort ( ) {
DListNode soFar = null;
for (DListNode p=myHead; p!=null; p=p.myNext) {
soFar = insert (p, soFar);
}
return new IntList (soFar);
}
// values will be in decreasing order.
private DListNode insert (DListNode p, DListNode head) {
DListNode q=new DListNode(p.myItem);
if(head==null){
head=q;
return head;
}
if(q.myItem>=head.myItem){
DListNode te=head;
q.myNext=te;
te.myPrev=q;
q=head;
return head;
}
DListNode a;
boolean found=false;
for(a=head; a!=null;){
if(a.myItem<q.myItem){
found=true;
break;
}
else{
a=a.myNext;
}
}
if(found==false){
DListNode temp=myTail;
temp.myNext=q;
q.myPrev=temp;
myTail=q;
return head;
}
if(found==true){
DListNode t;
t=a.myPrev;
a.myPrev=q;
t.myNext=q;
q.myPrev=t;
q.myNext=a;
}
return head;
}
Your code is a bit hard to read through but I noticed a few problems
First:
handling the case where you are inserting a number at the head of the list:
if(q.myItem>=head.myItem){
DListNode te=head;
q.myNext=te;
te.myPrev=q;
q=head;
return head;
}
specifically the line q=head; and the return. q=head can be removed, and it should return q not head because q is the new head. I think what you meant to do was head=q; return head;. The current code will essentially add the new node on the front but never return the updated head so they will "fall off the edge" in a way.
Second:
I am assuming myTail is some node reference you are keeping like myHead to the original list. I don't think you want to be using it like you are for the sorted list you are constructing. When you loop through looking for the place to insert in the new list, use that to determine the tail reference and use that instead.
DListNode lastCompared = null;
for(a=head; a!=null; a=a.myNext) {
lastCompared = a;
if(a.myItem<q.myItem) {
break;
}
}
if( a )
{
// insert node before a
...
}
else
{
// smallest value yet, throw on the end
lastCompared.myNext = q;
q.myPrev = lastCompared;
return head;
}
Finally make sure myPrev and myNext are being properly initialized to null in the constructor for DListNode.
disclaimer I didn't get a chance to test the code I added here, but hopefully it at least gets you thinking about the solution.
A couple stylistic notes (just a sidenote):
the repeated if->return format is not the cleanest in my opinion.
I generally try and limit the exit points in functions
There are a lot of intermediate variables being used and the names are super
ambiguous. At the very least try and use some more descriptive
variable names.
comments are always a good idea. Just make sure they don't just explain what the code is doing - instead try and
convey thought process and what is trying to be accomplished.