Author: Tech Corner

MongoDB

Include or Exclude Fields to Return from a Query

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The document can specify the inclusion of fields or the exclusion of fields. The specifications have the following forms.

  • Specify to include a field – 1 or TRUE
  • Specify to suppression/Exclude a field – 0 or FALSE
     db.users.find( { Name: 'Himen Patel' }, { Name: 1, Email: 1 } )

    In the result set, only the Name and Email fields and, by default, the _id field returns in the matching document (users). To remove the _id field from the results specifying it in exclusion.

     db.users.find( { Name: 'Himen Patel' }, { Name: 1, Email: 1, _id:0 } )
    MongoDB

    Remove Documents using Mongo Shell

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    The db.collection.remove() method removes documents from a collection.

    • You can remove all documents from a collection.
    • Remove all documents that match a condition.
    • Or limit the operation to remove just a single document.
     db.users.remove({})  //Remove All Documents  
     db.users.remove({Name : "Himen Patel" })  //Remove Documents that Match a Condition  
     db.users.remove({Name : "Himen Patel" },1 )  //Remove a Single Document that Matches a Condition
    MongoDB

    Upsert Option using Mongo Shell

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    By default, if no document matches the update query, the update() method does nothing.

    However, by specifying upsert: true, the update() method either updates matching document or documents, or inserts a new document using the update specification if no matching document exists.

    The following operation either updates a matching document by replacing it with a new document or adds a new document if no matching document exists.

     > db.users.update(  
     ...  { Name : "Hymen Patel" },  
     ...    {  
     ...  "Name": "Himen Paatel",  
     ...  "Email": "email2himen@dotnet-funda.com",  
     ...  "Address1": "1257 Commons Drive",  
     ...  "City": "Cooperstown",  
     ...  "Zip Code": "13326",  
     ...  "Country": "USA"  
     ...    },  
     ... { upsert: true }  
     ... )

    The update operation returns a WriteResult object which contains the status of the operation, including whether the db.collection.update() method modified an existing document or added a new document.

     WriteResult({  
         "nMatched" : 0,  
         "nUpserted" : 1,  
         "nModified" : 0,  
         "_id" : ObjectId("561324b1b6bb748311f00aac")  
     })

    Specify upsert: true for the update specific fields operation

     db.users.update(   
          { Name : "Himen Patel" },   
            {$set :   
            { "Email" : "admin@dotnet-fundamentals.com"} },  
           {upsert: true}  
     )
    MongoDB

    Replace a document using Mongo Shell

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    The following operation replaces the document with item equal to “Himen Patel”. The newly replaced document will only contain the the _id field and the fields in the replacement document.

     > db.users.update(  
     ...  { Name : "Himen Patel" },  
     ...    {  
     ...  "Name": "Himen Paatel",  
     ...  "Email": "email2himen@dotnet-funda.com",  
     ...  "Address1": "1257 Commons Drive",  
     ...  "City": "Cooperstown",  
     ...  "Zip Code": "13326",  
     ...  "Country": "USA"  
     ...    }  
     ... )

    A successful update of the document returns the following object.

     WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })