Thanks for your help Mike. Much appreciated.
I dont store rows/columns in JSON format. The schema is exactly that of a
specific java class, where the rowkey is a unique object identifier with
the class type encoded into it. Columns are the field names of the class
and the values are that of the object instance.
Did think about coprocessors but the schema is discovered a runtime and I
cant hard code it.
However, I still believe that filters might work. Had a look
at SingleColumnValueFilter and this filter is be able to target specific
column qualifiers with specific WritableByteArrayComparables.
But list comparators are still missing... So I guess the only way is to
write these comparators?
Do you follow my reasoning? Will it work?
On Fri, Jun 28, 2013 at 12:58 AM, Michael Segel
<michael_se...@hotmail.com>wrote:
> Ok...
>
> If you want to do type checking and schema enforcement...
>
> You will need to do this as a coprocessor.
>
> The quick and dirty way... (Not recommended) would be to hard code the
> schema in to the co-processor code.)
>
> A better way... at start up, load up ZK to manage the set of known table
> schemas which would be a map of column qualifier to data type.
> (If JSON then you need to do a separate lookup to get the records schema)
>
> Then a single java class that does the look up and then handles the known
> data type comparators.
>
> Does this make sense?
> (Sorry, kinda was thinking this out as I typed the response. But it should
> work )
>
> At least it would be a design approach I would talk. YMMV
>
> Having said that, I expect someone to say its a bad idea and that they
> have a better solution.
>
> HTH
>
> -Mike
>
> On Jun 27, 2013, at 5:13 PM, Kristoffer Sjögren <sto...@gmail.com> wrote:
>
> > I see your point. Everything is just bytes.
> >
> > However, the schema is known and every row is formatted according to this
> > schema, although some columns may not exist, that is, no value exist for
> > this property on this row.
> >
> > So if im able to apply these "typed comparators" to the right cell values
> > it may be possible? But I cant find a filter that target specific
> columns?
> >
> > Seems like all filters scan every column/qualifier and there is no way of
> > knowing what column is currently being evaluated?
> >
> >
> > On Thu, Jun 27, 2013 at 11:51 PM, Michael Segel
> > <michael_se...@hotmail.com>wrote:
> >
> >> You have to remember that HBase doesn't enforce any sort of typing.
> >> That's why this can be difficult.
> >>
> >> You'd have to write a coprocessor to enforce a schema on a table.
> >> Even then YMMV if you're writing JSON structures to a column because
> while
> >> the contents of the structures could be the same, the actual strings
> could
> >> differ.
> >>
> >> HTH
> >>
> >> -Mike
> >>
> >> On Jun 27, 2013, at 4:41 PM, Kristoffer Sjögren <sto...@gmail.com>
> wrote:
> >>
> >>> I realize standard comparators cannot solve this.
> >>>
> >>> However I do know the type of each column so writing custom list
> >>> comparators for boolean, char, byte, short, int, long, float, double
> >> seems
> >>> quite straightforward.
> >>>
> >>> Long arrays, for example, are stored as a byte array with 8 bytes per
> >> item
> >>> so a comparator might look like this.
> >>>
> >>> public class LongsComparator extends WritableByteArrayComparable {
> >>> public int compareTo(byte[] value, int offset, int length) {
> >>> long[] values = BytesUtils.toLongs(value, offset, length);
> >>> for (long longValue : values) {
> >>> if (longValue == val) {
> >>> return 0;
> >>> }
> >>> }
> >>> return 1;
> >>> }
> >>> }
> >>>
> >>> public static long[] toLongs(byte[] value, int offset, int length) {
> >>> int num = (length - offset) / 8;
> >>> long[] values = new long[num];
> >>> for (int i = offset; i < num; i++) {
> >>> values[i] = getLong(value, i * 8);
> >>> }
> >>> return values;
> >>> }
> >>>
> >>>
> >>> Strings are similar but would require charset and length for each
> string.
> >>>
> >>> public class StringsComparator extends WritableByteArrayComparable {
> >>> public int compareTo(byte[] value, int offset, int length) {
> >>> String[] values = BytesUtils.toStrings(value, offset, length);
> >>> for (String stringValue : values) {
> >>> if (val.equals(stringValue)) {
> >>> return 0;
> >>> }
> >>> }
> >>> return 1;
> >>> }
> >>> }
> >>>
> >>> public static String[] toStrings(byte[] value, int offset, int length)
> {
> >>> ArrayList<String> values = new ArrayList<String>();
> >>> int idx = 0;
> >>> ByteBuffer buffer = ByteBuffer.wrap(value, offset, length);
> >>> while (idx < length) {
> >>> int size = buffer.getInt();
> >>> byte[] bytes = new byte[size];
> >>> buffer.get(bytes);
> >>> values.add(new String(bytes));
> >>> idx += 4 + size;
> >>> }
> >>> return values.toArray(new String[values.size()]);
> >>> }
> >>>
> >>>
> >>> Am I on the right track or maybe overlooking some implementation
> details?
> >>> Not really sure how to target each comparator to a specific column
> value?
> >>>
> >>>
> >>> On Thu, Jun 27, 2013 at 9:21 PM, Michael Segel <
> >> michael_se...@hotmail.com>wrote:
> >>>
> >>>> Not an easy task.
> >>>>
> >>>> You first need to determine how you want to store the data within a
> >> column
> >>>> and/or apply a type constraint to a column.
> >>>>
> >>>> Even if you use JSON records to store your data within a column, does
> an
> >>>> equality comparator exist? If not, you would have to write one.
> >>>> (I kinda think that one may already exist...)
> >>>>
> >>>>
> >>>> On Jun 27, 2013, at 12:59 PM, Kristoffer Sjögren <sto...@gmail.com>
> >> wrote:
> >>>>
> >>>>> Hi
> >>>>>
> >>>>> Working with the standard filtering mechanism to scan rows that have
> >>>>> columns matching certain criterias.
> >>>>>
> >>>>> There are columns of numeric (integer and decimal) and string types.
> >>>> These
> >>>>> columns are single or multi-valued like "1", "2", "1,2,3", "a", "b"
> or
> >>>>> "a,b,c" - not sure what the separator would be in the case of list
> >> types.
> >>>>> Maybe none?
> >>>>>
> >>>>> I would like to compose the following queries to filter out rows that
> >>>> does
> >>>>> not match.
> >>>>>
> >>>>> - contains(String column, String value)
> >>>>> Single valued column that String.contain() provided value.
> >>>>>
> >>>>> - equal(String column, Object value)
> >>>>> Single valued column that Object.equals() provided value.
> >>>>> Value is either string or numeric type.
> >>>>>
> >>>>> - greaterThan(String column, java.lang.Number value)
> >>>>> Single valued column that > provided numeric value.
> >>>>>
> >>>>> - in(String column, Object value...)
> >>>>> Multi-valued column have values that Object.equals() all provided
> >>>> values.
> >>>>> Values are of string or numeric type.
> >>>>>
> >>>>> How would I design a schema that can take advantage of the already
> >>>> existing
> >>>>> filters and comparators to accomplish this?
> >>>>>
> >>>>> Already looked at the string and binary comparators but fail to see
> how
> >>>> to
> >>>>> solve this in a clean way for multi-valued column values.
> >>>>>
> >>>>> Im aware of custom filters but would like to avoid it if possible.
> >>>>>
> >>>>> Cheers,
> >>>>> -Kristoffer
> >>>>
> >>>>
> >>
> >>
>
>
