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How to determine whether a field exists in MongoDB?
<p>You need to use $exists operator to determine whether a field exists in MongoDB. Let us first create a collection with documents</p><pre class="prettyprint notranslate">> db.determineFieldExistsDemo.insertOne({"ClientName":"John"}); { "acknowledged" : true, "insertedId" : ObjectId("5c9eb245d628fa4220163b75") } > db.determineFieldExistsDemo.insertOne({"ClientName":"Larry","ClientAge":23}); { "acknowledged" : true, "insertedId" : ObjectId("5c9eb25cd628fa4220163b76") } > db.determineFieldExistsDemo.insertOne({"ClientName":"Mike","ClientCountryName":"UK"}); { "acknowledged" : true, "insertedId" : ObjectId("5c9eb26fd628fa4220163b77") } > db.determineFieldExistsDemo.insertOne({"ClientName":"Sam","ClientAge":24}); { "acknowledged" : true, "insertedId" : ObjectId("5c9eb286d628fa4220163b78") }</pre><p>Following is the query to display all documents from a collection with the help of find() method</p><pre class="prettyprint notranslate">> db.determineFieldExistsDemo.find().pretty();</pre><p>This will produce the following output</p><pre class="result notranslate">{ "_id" : ObjectId("5c9eb245d628fa4220163b75"), "ClientName" : "John" } { "_id" : ObjectId("5c9eb25cd628fa4220163b76"), "ClientName" : "Larry", "ClientAge" : 23 } { "_id" : ObjectId("5c9eb26fd628fa4220163b77"), "ClientName" : "Mike", "ClientCountryName" : "UK" } { "_id" : ObjectId("5c9eb286d628fa4220163b78"), "ClientName" : "Sam", "ClientAge" : 24 }</pre><p>Following is the query to determine whether a field exists</p><pre class="prettyprint notranslate">> db.determineFieldExistsDemo.find({ClientCountryName:{$exists:true}}).pretty();</pre><p>This will produce the following output</p><pre class="result notranslate">{ "_id" : ObjectId("5c9eb26fd628fa4220163b77"), "ClientName" : "Mike", "ClientCountryName" : "UK" }</pre>
Updated on 30-Jul-2019 22:30:25
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