我正在使用mongo java驱动程序并尝试计算特定字段不为空或不存在的所有文档。这是我到目前为止所做的:
String field = "myfieldname";
BasicDBObject notNull = new BasicDBObject(field,BasicDBObject("$ne",null));
List<Object> condition = Arrays.asList(notNull,1,0);
BasicDBObject aggregation = new BasicDBObject("$cond",condition);
// boiler plate code to lookup my database/collection and pass the aggregation to it
这似乎不起作用。
编辑: 感谢Rob Moore的帮助。以下是我最终使其工作的原因
BasicDBObject ifNull = new BasicDBObject('$ifNull',Arrays.asList('$'+field,null));
BasicDBObject neq = new BasicDBObject('$ne', Arrays.asList(null,ifNull));
return new BasicDBObject('$cond', Arrays.asList(neq,1,0);
答案 0 :(得分:5)
这是一个实现我认为你所追求的逻辑的应用程序。它使用Asynchronous Java Driver's辅助类来帮助构建正确的管道。在代码的最后,我们插入了99个文档。 33具有空字段值,33具有值,33没有值。该应用程序共有66个,我认为这是你所追求的结果。
/*
* Copyright 2013 - Allanbank Consulting, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package stackoverflow;
import static com.allanbank.mongodb.builder.AggregationGroupField.set;
import static com.allanbank.mongodb.builder.AggregationGroupId.constantId;
import static com.allanbank.mongodb.builder.AggregationProjectFields.include;
import static com.allanbank.mongodb.builder.Find.ALL;
import static com.allanbank.mongodb.builder.expression.Expressions.cond;
import static com.allanbank.mongodb.builder.expression.Expressions.constant;
import static com.allanbank.mongodb.builder.expression.Expressions.eq;
import static com.allanbank.mongodb.builder.expression.Expressions.field;
import static com.allanbank.mongodb.builder.expression.Expressions.ifNull;
import static com.allanbank.mongodb.builder.expression.Expressions.set;
import java.io.IOException;
import java.util.Random;
import com.allanbank.mongodb.MongoClient;
import com.allanbank.mongodb.MongoCollection;
import com.allanbank.mongodb.MongoFactory;
import com.allanbank.mongodb.bson.builder.BuilderFactory;
import com.allanbank.mongodb.bson.builder.DocumentBuilder;
import com.allanbank.mongodb.bson.element.ArrayElement;
import com.allanbank.mongodb.bson.element.ObjectId;
import com.allanbank.mongodb.builder.Aggregate;
/**
* Count the number of documents that have a particular field.
*
* @see <a
* href="http://stackoverflow.com/questions/20964169/mongo-java-conditional-sum-if-exists">StackOverflow
* Question</a>
*
* @copyright 2013, Allanbank Consulting, Inc., All Rights Reserved
*/
public class SumIfExists {
/**
* A source of no so random values. Use a fixed seed to always get the same
* values for fields.
*/
private final static Random random = new Random(123456789L);
/**
* The handle to the MongoDB client. We assume MongoDB is running on your
* machine on the default port of 27017.
*/
private final static MongoClient client = MongoFactory
.createClient("mongodb://localhost:27017/");
/** The collection we will be using. */
private final static MongoCollection theCollection = client.getDatabase(
"db").getCollection("collection");
/**
* Run the demo.
*
* @param args
* Command line arguments. Ignored.
* @throws IOException
* On a failure closing the MongoCLient.
*/
public static void main(String[] args) throws IOException {
// Build the aggregation document/command.
Aggregate.Builder builder = Aggregate.builder();
// From the StackOverflow Question.
String fieldName = "myfieldname";
// A token ObjectId to use in comparisons for the null field.
ObjectId nullToken = new ObjectId();
builder.project(
include("a", "b", "c", "etc"),
set("myfieldnameExists",
cond(eq(ifNull(field(fieldName), constant(nullToken)),
constant(nullToken)), constant(0), constant(1))));
builder.group(constantId("a"), set("count").sum("myfieldnameExists"));
System.out.println(new ArrayElement("$pipeline", builder.build()
.getPipeline()));
// Insert some documents to test with.
theCollection.delete(ALL);
for (int i = 0; i < 99; ++i) {
DocumentBuilder doc = BuilderFactory.start();
if (i % 3 == 0) {
doc.addNull(fieldName);
}
else if (i % 3 == 1) {
doc.add(fieldName, random.nextDouble());
}
// else if (i % 3 == 2) -- Field does not exist.
doc.add("a", random.nextBoolean());
doc.add("b", random.nextInt());
doc.add("c", random.nextLong());
doc.add("etc", random.nextLong());
theCollection.insert(doc);
}
// Run the aggregation.
System.out.println(theCollection.aggregate(builder));
}
}
代码的输出是:
'$pipeline' : [
{
'$project' : {
a : 1,
b : 1,
c : 1,
etc : 1,
myfieldnameExists : {
'$cond' : [
{
'$eq' : [
{
'$ifNull' : [
'$myfieldname',
ObjectId('52cb94836c4a28185433c4d3')
]
},
ObjectId('52cb94836c4a28185433c4d3')
]
},
0,
1
]
}
}
},
{
'$group' : {
'_id' : 'a',
count : { '$sum' : '$myfieldnameExists' }
}
}
]
[{
'_id' : 'a',
count : 66
}]
我关门了吗? 罗布。