问答:mongo java条件求和,如果不为null - 问答

1 个回答

这是一个实现我认为你所追求的逻辑的应用程序.它使用异步Java驱动程序的帮助程序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 }] 我接近了吗？抢.

2023-02-06 10:16 回答手机用户2602918611