db.inventory.insertMany([

   { item: "journal", qty: 25, size: { h: 14, w: 21, uom: "cm" }, status: "A" },

   { item: "notebook", qty: 50, size: { h: 8.5, w: 11, uom: "in" }, status: "A" },

   { item: "paper", qty: 100, size: { h: 8.5, w: 11, uom: "in" }, status: "D" },

   { item: "planner", qty: 75, size: { h: 22.85, w: 30, uom: "cm" }, status: "D" },

   { item: "postcard", qty: 45, size: { h: 10, w: 15.25, uom: "cm" }, status: "A" }

])

db.inventory.find({})

db.inventory.find({

    status:"D"

    })

db.inventory.find({

status:{

    $in:["A","D"]

    }

    }

)

db.inventory.find({

    status:"A",

    qty:{$lt:30}

    })

db.inventory.find({

    $or:[

    {status:"A"},

    {qty:30}

    ]

    })

db.inventory.find({

    status:"A",

    $or:[

    {qty:{

        $lt:30

        }},

    {item:/^p/}

    ]

    })

Select All Documents in a Collection

To select all documents in the collection, pass an empty document as the query filter parameter to the find method. The query filter parameter determines the select criteria:

db.inventory.find( {} )

These operation corresponds to the following SQL statement:

SELECT * FROM inventory

Specify Equality Condition

{ <field1>: <value1>, ... }

The following example selects from the inventory collection all documents where the status equals "D":

db.inventory.find( { status: "D" } )

This operation corresponds to the following SQL statement:

SELECT * FROM inventory WHERE status = "D"

Specify Conditions Using Query Operators

{ <field1>: { <operator1>: <value1> }, ... }

The following example retrieves all documents from the inventory collection where status equals either"A" or "D":

db.inventory.find( { status: { $in: [ "A", "D" ] } } )

Although you can express this query using the $or operator, use the $in operator rather than the $oroperator when performing equality checks on the same field.

The operation corresponds to the following SQL statement:

SELECT * FROM inventory WHERE status in ("A", "D")

Refer to the Query and Projection Operators document for the complete list of MongoDB query operators.

Specify AND Conditions

A compound query can specify conditions for more than one field in the collection’s documents. Implicitly, a logical AND conjunction connects the clauses of a compound query so that the query selects the documents in the collection that match all the conditions.

The following example retrieves all documents in the inventory collection where the status equals "A"and qty is less than ($lt) 30:

db.inventory.find( { status: "A", qty: { $lt: 30 } } )

The operation corresponds to the following SQL statement:

SELECT * FROM inventory WHERE status = "A" AND qty < 30

See comparison operators for other MongoDB comparison operators.

Specify OR Conditions

Using the $or operator, you can specify a compound query that joins each clause with a logical ORconjunction so that the query selects the documents in the collection that match at least one condition.

The following example retrieves all documents in the collection where the status equals "A" or qty is less than ($lt) 30:

db.inventory.find( { $or: [ { status: "A" }, { qty: { $lt: 30 } } ] } )

The operation corresponds to the following SQL statement:

SELECT * FROM inventory WHERE status = "A" OR qty < 30

db.inventory.find( {

     status: "A",

     $or: [ { qty: { $lt: 30 } }, { item: /^p/ } ]

} )

SELECT * FROM inventory WHERE status = "A" AND ( qty < 30 OR item LIKE "p%")

Additional Query Tutorials

For additional query examples, see:

• Query on Embedded/Nested Documents
• Query an Array
• Query an Array of Embedded Documents
• Project Fields to Return from Query
• Query for Null or Missing Fields

Behavior

Additional Methods

The following methods can also read documents from a collection: