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I am very new to MongoDB and its Java... SDK? Api? I have a very simple question, but I haven't been able to find a satisfactory answer.
Let's say I have a collection of instances that are like:
{
"_id": {
"$oid": "5156171e5d451c136236e738"
},
"_types": [
"Sample"
],
"last_z": {
"$date": "2012-12-30T09:12:12.250Z"
},
"last": {
"$date": "2012-12-30T04:12:12.250Z"
},
"section": "5156171e5d451c136236e70f",
"s_mac": "AA:AA:AA:AA:AA:AA",
"_cls": "Sample",
}
And I have a hard-coded Java list:
static List<String> MAC_LIST = Arrays.asList("90:27:E4:0E:3D:D2", "A8:26:D9:E6:1D:8B");
What I would like to know is how to query the MongoDB so it will give me all the objects whose s_mac field has a value that appears in the MAC_LIST List.
I'm guessing I should use the $in operator, but I don't know how to translate it to Java code.
Any hint or link to pages with explanations of the use of the $in operator through the Java SDK would be appreciated!
823
To query if the array field contains at least one element with the specified value, use the filter { <field>: <value> } where <value> is the element value. To specify conditions on the elements in the array field, use query operators in the query filter document: { <array field>: { <operator1>: <value1>, ... } }
Filter MongoDB Array Element Using $Filter Operator This operator uses three variables: input – This represents the array that we want to extract. cond – This represents the set of conditions that must be met. as – This optional field contains a name for the variable that represent each element of the input array.
You can select a single field in MongoDB using the following syntax: db. yourCollectionName. find({"yourFieldName":yourValue},{"yourSingleFieldName":1,_id:0});
MongoDB provides the find() that is used to find multiple values or documents from the collection. The find() method returns a cursor of the result set and prints all the documents. To find the multiple values, we can use the aggregation operations that are provided by MongoDB itself.
Here is a contrived example that works for me (driver version 2.10.1) - you can adjust the IP address and run it as is to check if you get the same outcome:
public void gss() throws Exception{
MongoClient mongo = new MongoClient("192.168.1.1");
DB db = mongo.getDB("test");
DBCollection collection = db.getCollection("stackoverflow");
DBObject o1 = new BasicDBObject();
o1.put("s_mac", "AA:AA:AA:AA:AA:AA");
o1.put("_cls", "Sample1");
DBObject o2 = new BasicDBObject();
o2.put("s_mac", "90:27:E4:0E:3D:D2");
o2.put("_cls", "Sample2");
DBObject o3 = new BasicDBObject();
o3.put("s_mac", "A8:26:D9:E6:1D:8B");
o3.put("_cls", "Sample3");
collection.insert(o1, o2, o3);
System.out.println(collection.find().count());
List<String> MAC_LIST = Arrays.asList("90:27:E4:0E:3D:D2", "A8:26:D9:E6:1D:8B");
System.out.println(collection.find(new BasicDBObject("s_mac", new BasicDBObject("$in", MAC_LIST))).count());
}
It inserts the following documents:
{ "_id" : ObjectId("5159ff98567e143bff0668e9"),
"s_mac" : "AA:AA:AA:AA:AA:AA",
"_cls" : "Sample1"
}
{ "_id" : ObjectId("5159ff98567e143bff0668ea"),
"s_mac" : "90:27:E4:0E:3D:D2",
"_cls" : "Sample2"
}
{ "_id" : ObjectId("5159ff98567e143bff0668eb"),
"s_mac" : "A8:26:D9:E6:1D:8B",
"_cls" : "Sample3"
}
A call to collection.find().count() returns 3 and a call to collection.find(new BasicDBObject("s_mac", new BasicDBObject("$in", MAC_LIST))).count() returns 2 which I think is what you expected.
78
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