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MongoDB null value query

Posted on 2011-09-17
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Last Modified: 2016-02-10
Hi,

There are records in one of my Mongodb collection 'exmple' (please see attached code).

I would like to have Java queries so that I can get the records for each of the following scenarios:

1) records whose "nextfetchtime" field is not exist;

2) records whose "nextfetchtime" field has value of null;

Thanks.
{ "_id" : { "$oid" : "4e72eac3e4b0a2c48b0eb84d"} , "code" : "5g9a4gini94404mp1inoip5ni4gpcgn4gnin50i0ci5a0n95g555o4pgg1m45o15" , "path" : "/data2/data/htmlsource/2011-09-16/dianpingcom/" , "finishtime" : 1316154241099 , "nextfetchtime" : 1318746051658 , "codeTime" : 1316154051696 , "predicted" : false}
{ "_id" : { "$oid" : "4e7564247af2f2aa38b3fbe8"} , "code" : "mw2Da0toDk6xhkz6IVNxmEQSsQ3nLnJ84Ccxvw0734i5Hv5auTHk5aQtmUq1KxhY" , "path" : "c:/data/berkeley/database/parsedcodedb-bak/2011-07-03/dianping" , "finishtime" : 1316316196568}
{ "_id" : { "$oid" : "4e7564377af2587c0e06e5df"} , "code" : "fl6Q3Nw3BCMrX5LxHoY49llQ81vfYtW0yTGec9arAHYch8yvDvGPJ37LOzKwOOgc" , "path" : "c:/data/berkeley/database/parsedcodedb-bak/2011-07-03/dianping" , "finishtime" : 1316316215222}
{ "_id" : { "$oid" : "4e7568e07af237357a034671"} , "code" : "QfDfFpWqBHAtJYkJbMdTWFl5UrLx6lp96bdOFGzIOs0m1RlqRPxhIC0RA9ONB2yh" , "path" : "c:/data/berkeley/database/parsedcodedb-bak/2011-07-03/dianping" , "finishtime" : 1316317408821 , "nextfetchtime" :  null }

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Question by:wsyy
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Kevin Cross earned 125 total points
ID: 36556761
Hi.

Is this a homework assignment?

In any case, if you are going to be working with Java and MongoDB, you probably want to start with the tutorial here: http://www.mongodb.org/display/DOCS/Java+Tutorial

The first step is get the MongoDB Java Driver. This API reference along with the tutorial should be helpful.

Hope that helps!

Please give the code a try yourself first, then post back specific challenges you are having. If it is a compilation or run-time error please post details. For the latter, please post the full stack trace to a code snippet. If the issue is the code runs, but does not yield the proper output, please give an sample with current results alongside expected ones.

We can guide you from there. This way, you will "learn" what you need going forward.

Best regards and happy coding,

Kevin
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