Row keys must be unique. If your usernames are not unique and you want to be able to query on them, you either need to figure out a way to make them unique or treat the username rows themselves as indices, which refer to a set of actually unique identifiers for users.
On Sun, Apr 11, 2010 at 11:12 AM, vineet daniel <vineetdan...@gmail.com> wrote: > its not a problem its a scenario, which we need to handle. And all I am > trying to do is to achieve what is not there with API i.e a workaroud. > > On Sun, Apr 11, 2010 at 11:06 PM, Benjamin Black <b...@b3k.us> wrote: >> >> A system that permits multiple people to have the same username has a >> serious problem. >> >> On Sun, Apr 11, 2010 at 6:12 AM, vineet daniel <vineetdan...@gmail.com> >> wrote: >> > How to handle same usernames. Otherwise seems fine to me. >> > >> > On Sun, Apr 11, 2010 at 6:17 PM, Dop Sun <su...@dopsun.com> wrote: >> >> >> >> Hi, >> >> >> >> >> >> >> >> As far as I can see it, the Cassandra API currently supports criterias >> >> on: >> >> >> >> Token – Key – Super Column Name (if applicable) - Column Names >> >> >> >> >> >> >> >> I guess Token is not usually used for the day to day queries, so, Key >> >> and >> >> Column Names are normally used for querying. For the user name and >> >> password >> >> case, I guess it can be done like this: >> >> >> >> >> >> >> >> Define a CF as UserAuth with type as Super, and Key is user name, while >> >> password can be the SuperKeyName. So, while you receive the user name >> >> and >> >> password from the UI (or any other methods), it can be queried via: >> >> multiget_slice or get_range_slices, if there are anything returned, >> >> means >> >> that the user name and password matches. >> >> >> >> >> >> >> >> If not using the super column name, and put the password as the column >> >> name, the column name usually not used for these kind of discretionary >> >> values (actually, I don’t see any definitive documents on how to use >> >> the >> >> column Names and Super Columns, flexibility is the good of Cassandra, >> >> or is >> >> it bad if abused? :P) >> >> >> >> >> >> >> >> Not sure whether this is the best way, but I guess it will work. >> >> >> >> >> >> >> >> Regards, >> >> >> >> Dop >> >> >> >> >> >> >> >> From: Lucifer Dignified [mailto:vineetdan...@gmail.com] >> >> Sent: Sunday, April 11, 2010 5:33 PM >> >> To: user@cassandra.apache.org >> >> Subject: Re: How to perform queries on Cassandra? >> >> >> >> >> >> >> >> Hi Benjamin >> >> >> >> I'll try to make it more clear to you. >> >> We have a user table with fields 'id', 'username', and 'password'. Now >> >> if >> >> use the ideal way to store key/value, like : >> >> username : vineetdaniel >> >> timestamp >> >> password : <password> >> >> timestamp >> >> >> >> second user : >> >> >> >> username: <seconduser> >> >> timestamp >> >> password:<password> >> >> >> >> and so on, here what i assume is that as we cannot make search on >> >> values >> >> (as confirmed by guys on cassandra forums) we are not able to perform >> >> robust >> >> 'where' queries. Now what i propose is this. >> >> >> >> Rather than using a static values for column names use values itself >> >> and >> >> unique key as identifier. So, the above example when put in as per me >> >> would >> >> be. >> >> >> >> vineetdaniel : vineetdaniel >> >> timestamp >> >> >> >> <password>:<password> >> >> timestamp >> >> >> >> second user >> >> seconduser:seconduser >> >> timestamp >> >> >> >> password:password >> >> timestamp >> >> >> >> By using above methodology we can simply make search on keys itself >> >> rather >> >> than going into using different CF's. But to add further, this cannot >> >> be >> >> used for every situation. I am still exploring this, and soon will be >> >> updating the group and my blog with information pertaining to this. As >> >> cassandra is new, I think every idea or experience should be shared >> >> with the >> >> community. >> >> >> >> I hope I example is clear this time. Should you have any queries feel >> >> free >> >> to revert. >> >> >> >> On Sun, Apr 11, 2010 at 2:01 PM, Benjamin Black <b...@b3k.us> wrote: >> >> >> >> Sorry, I don't understand your example. >> >> >> >> On Sun, Apr 11, 2010 at 12:54 AM, Lucifer Dignified >> >> <vineetdan...@gmail.com> wrote: >> >> > Benjamin I quite agree to you, but what in case of duplicate >> >> > usernames, >> >> > suppose if I am not using unique names as in email id's . If we have >> >> > duplicacy in usernames we cannot use it for key, so what should be >> >> > the >> >> > solution. I think keeping incremental numeric id as key and keeping >> >> > the >> >> > name >> >> > and value same in the column family. >> >> > >> >> > Example : >> >> > User1 has password as 123456 >> >> > >> >> > Cassandra structure : >> >> > >> >> > 1 as key >> >> > user1 - column name >> >> > value - user1 >> >> > 123456 - column name >> >> > value - 123456 >> >> > >> >> > I m thinking of doing it this way for my applicaton, this way i can >> >> > run >> >> > different sorts of queries too. Any feedback on this is welcome. >> >> > >> >> > On Sun, Apr 11, 2010 at 1:13 PM, Benjamin Black <b...@b3k.us> wrote: >> >> >> >> >> >> You would have a Column Family, not a column for that; let's call it >> >> >> the Users CF. You'd use username as the row key and have a column >> >> >> called 'password'. For your example query, you'd retrieve row key >> >> >> 'usr2', column 'password'. The general pattern is that you create >> >> >> CFs >> >> >> to act as indices for each query you want to perform. There is no >> >> >> equivalent to a relational store to perform arbitrary queries. You >> >> >> must structure things to permit the queries of interest. >> >> >> >> >> >> >> >> >> b >> >> >> >> >> >> On Sat, Apr 10, 2010 at 8:34 PM, dir dir <sikerasa...@gmail.com> >> >> >> wrote: >> >> >> > I have already read the API spesification. Honestly I do not >> >> >> > understand >> >> >> > how to use it. Because there are not an examples. >> >> >> > >> >> >> > For example I have a column like this: >> >> >> > >> >> >> > UserName Password >> >> >> > usr1 abc >> >> >> > usr2 xyz >> >> >> > usr3 opm >> >> >> > >> >> >> > suppose I want query the user's password using SQL in RDBMS >> >> >> > >> >> >> > Select Password From Users Where UserName = "usr2"; >> >> >> > >> >> >> > Now I want to get the password using OODBMS DB4o Object Query and >> >> >> > Java >> >> >> > >> >> >> > ObjectSet QueryResult = db.query(new Predicate() >> >> >> > { >> >> >> > public boolean match(Users Myusers) >> >> >> > { >> >> >> > return Myuser.getUserName() == "usr2"; >> >> >> > } >> >> >> > }); >> >> >> > >> >> >> > After we get the Users instance in the QueryResult, hence we can >> >> >> > get >> >> >> > the >> >> >> > usr2's password. >> >> >> > >> >> >> > How we perform this query using Cassandra API and Java?? >> >> >> > Would you tell me please?? Thank You. >> >> >> > >> >> >> > Dir. >> >> >> > >> >> >> > >> >> >> > On Sat, Apr 10, 2010 at 11:06 AM, Paul Prescod <p...@prescod.net> >> >> >> > wrote: >> >> >> >> >> >> >> >> No. Cassandra has an API. >> >> >> >> >> >> >> >> http://wiki.apache.org/cassandra/API >> >> >> >> >> >> >> >> On Fri, Apr 9, 2010 at 8:00 PM, dir dir <sikerasa...@gmail.com> >> >> >> >> wrote: >> >> >> >> > Does Cassandra has a default query language such as SQL in >> >> >> >> > RDBMS >> >> >> >> > and Object Query in OODBMS? Thank you. >> >> >> >> > >> >> >> >> > Dir. >> >> >> >> > >> >> >> >> > On Sat, Apr 10, 2010 at 7:01 AM, malsmith >> >> >> >> > <malsm...@treehousesystems.com> >> >> >> >> > wrote: >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> It's sort of an interesting problem - in RDBMS one relatively >> >> >> >> >> simple >> >> >> >> >> approach would be calculate a rectangle that is X km by Y km >> >> >> >> >> with >> >> >> >> >> User >> >> >> >> >> 1's >> >> >> >> >> location at the center. So the rectangle is UserX - 10KmX , >> >> >> >> >> UserY-10KmY to >> >> >> >> >> UserX+10KmX , UserY+10KmY >> >> >> >> >> >> >> >> >> >> Then you could query the database for all other users where >> >> >> >> >> that >> >> >> >> >> each >> >> >> >> >> user >> >> >> >> >> considered is curUserX > UserX-10Km and curUserX < UserX+10KmX >> >> >> >> >> and >> >> >> >> >> curUserY >> >> >> >> >> > UserY-10KmY and curUserY < UserY+10KmY >> >> >> >> >> * Not the 10KmX and 10KmY are really a translation from >> >> >> >> >> Kilometers >> >> >> >> >> to >> >> >> >> >> degrees of lat and longitude (that you can find on a google >> >> >> >> >> search) >> >> >> >> >> >> >> >> >> >> With the right indexes this query actually runs pretty well. >> >> >> >> >> >> >> >> >> >> Translating that to Cassandra seems a bit complex at first - >> >> >> >> >> but >> >> >> >> >> you >> >> >> >> >> could >> >> >> >> >> try something like pre-calculating a grid with the right >> >> >> >> >> resolution >> >> >> >> >> (like a >> >> >> >> >> square of 5KM per side) and assign every user to a particular >> >> >> >> >> grid >> >> >> >> >> ID. >> >> >> >> >> That >> >> >> >> >> way you just calculate with grid ID User1 is in then do a >> >> >> >> >> direct >> >> >> >> >> key >> >> >> >> >> lookup >> >> >> >> >> to get a list of the users in that same grid id. >> >> >> >> >> >> >> >> >> >> A second approach would be to have to column families -- one >> >> >> >> >> that >> >> >> >> >> maps >> >> >> >> >> a >> >> >> >> >> Latitude to a list of users who are at that latitude and a >> >> >> >> >> second >> >> >> >> >> that >> >> >> >> >> maps >> >> >> >> >> users who are at a particular longitude. You could do the >> >> >> >> >> same >> >> >> >> >> rectange >> >> >> >> >> calculation above then do a get_slice range lookup to get a >> >> >> >> >> list >> >> >> >> >> of >> >> >> >> >> users >> >> >> >> >> from range of latitude and a second list from the range of >> >> >> >> >> longitudes. >> >> >> >> >> You would then need to do a in-memory nested loop to find the >> >> >> >> >> list >> >> >> >> >> of >> >> >> >> >> users >> >> >> >> >> that are in both lists. This second approach could cause some >> >> >> >> >> trouble >> >> >> >> >> depending on where you search and how many users you really >> >> >> >> >> have >> >> >> >> >> -- >> >> >> >> >> some >> >> >> >> >> latitudes and longitudes have many many people in them >> >> >> >> >> >> >> >> >> >> So, it seems some version of a chunking / grid id thing would >> >> >> >> >> be >> >> >> >> >> the >> >> >> >> >> better approach. If you let people zoom in or zoom out - you >> >> >> >> >> could >> >> >> >> >> just >> >> >> >> >> have different column families for each level of zoom. >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> I'm stuck on a stopped train so -- here is even more code: >> >> >> >> >> >> >> >> >> >> static Decimal GetLatitudeMiles(Decimal lat) >> >> >> >> >> { >> >> >> >> >> Decimal f = 0.0M; >> >> >> >> >> lat = Math.Abs(lat); >> >> >> >> >> f = 68.99M; >> >> >> >> >> if (lat >= 0.0M && lat < 10.0M) { f = 68.71M; } >> >> >> >> >> else if (lat >= 10.0M && lat < 20.0M) { f = 68.73M; } >> >> >> >> >> else if (lat >= 20.0M && lat < 30.0M) { f = 68.79M; } >> >> >> >> >> else if (lat >= 30.0M && lat < 40.0M) { f = 68.88M; } >> >> >> >> >> else if (lat >= 40.0M && lat < 50.0M) { f = 68.99M; } >> >> >> >> >> else if (lat >= 50.0M && lat < 60.0M) { f = 69.12M; } >> >> >> >> >> else if (lat >= 60.0M && lat < 70.0M) { f = 69.23M; } >> >> >> >> >> else if (lat >= 70.0M && lat < 80.0M) { f = 69.32M; } >> >> >> >> >> else if (lat >= 80.0M) { f = 69.38M; } >> >> >> >> >> >> >> >> >> >> return f; >> >> >> >> >> } >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> Decimal MilesPerDegreeLatitude = >> >> >> >> >> GetLatitudeMiles(zList[0].Latitude); >> >> >> >> >> Decimal MilesPerDegreeLongitude = ((Decimal) >> >> >> >> >> Math.Abs(Math.Cos((Double) >> >> >> >> >> zList[0].Latitude))) * 24900.0M / 360.0M; >> >> >> >> >> dRadius = 10.0M // ten miles >> >> >> >> >> Decimal deltaLat = dRadius / MilesPerDegreeLatitude; >> >> >> >> >> Decimal deltaLong = dRadius / MilesPerDegreeLongitude; >> >> >> >> >> >> >> >> >> >> ps.TopLatitude = zList[0].Latitude - deltaLat; >> >> >> >> >> ps.TopLongitude = zList[0].Longitude - deltaLong; >> >> >> >> >> ps.BottomLatitude = zList[0].Latitude + deltaLat; >> >> >> >> >> ps.BottomLongitude = zList[0].Longitude + deltaLong; >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> On Fri, 2010-04-09 at 16:30 -0700, Paul Prescod wrote: >> >> >> >> >> >> >> >> >> >> 2010/4/9 Onur AKTAS <onur.ak...@live.com>: >> >> >> >> >> > ... >> >> >> >> >> > I'm trying to find out how do you perform queries with >> >> >> >> >> > calculations >> >> >> >> >> > on >> >> >> >> >> > the >> >> >> >> >> > fly without inserting the data as calculated from the >> >> >> >> >> > beginning. >> >> >> >> >> > Lets say we have latitude and longitude coordinates of all >> >> >> >> >> > users >> >> >> >> >> > and >> >> >> >> >> > we >> >> >> >> >> > have >> >> >> >> >> > Distance(from_lat, from_long, to_lat, to_long) function >> >> >> >> >> > which >> >> >> >> >> > gives distance between lat/longs pairs in kilometers. >> >> >> >> >> >> >> >> >> >> I'm not an expert, but I think that it boils down to >> >> >> >> >> "MapReduce" >> >> >> >> >> and >> >> >> >> >> "Hadoop". >> >> >> >> >> >> >> >> >> >> I don't think that there's any top-down tutorial on those two >> >> >> >> >> words, >> >> >> >> >> you'll have to research yourself starting here: >> >> >> >> >> >> >> >> >> >> * http://en.wikipedia.org/wiki/MapReduce >> >> >> >> >> >> >> >> >> >> * http://hadoop.apache.org/ >> >> >> >> >> >> >> >> >> >> * http://wiki.apache.org/cassandra/HadoopSupport >> >> >> >> >> >> >> >> >> >> I don't think it is all documented in any one place yet... >> >> >> >> >> >> >> >> >> >> Paul Prescod >> >> >> >> >> >> >> >> >> > >> >> >> >> > >> >> >> > >> >> >> > >> >> > >> >> > >> >> >> >> >> > > >
