Intermediate Mongo

Lesson Objectives

Let's go into a few more complex examples of how Mongo can be used. We'll cover the following:

1. Using intermediate find operators

2. Explaining update operators

3. Explaining upserts

4. Explaining multiple updates

Use intermediate find operators

To find all the documents in our collection that have a weight property greater than 700, we run:

db.employees.find(
    {
        weight : {
            $gt : 700
        }
    }
)

There are several comparisons we can perform

• $lt (less than)

• $lte (less than or equal to)

• $gt (greater than)

• $gte (greater than or equal to)

• $ne (not equal to)

• $exists (does the property exist on an object -- either true or false)

• $in (does the value exist within the given array)

If the field is an array, you can search for a match within that array

db.employees.find(
    {
        loves:'energon'
    }
)

If the object you pass into find() has more than one attribute, it will return documents that match both criteria. This is called an AND statement (like &&)

db.employees.find(
    {
        gender: 'm',
        weight: {
            $gt: 700
        }
    }
)

To find all documents that match at least one of a set of criteria, use an OR statement (like ||)

db.employees.find(
    {
        $or: [
            {
                loves: 'apple'
            },
            {
                weight: {
                    $lt: 500
                }
            }
        ]
    }
)

To find documents that have a value that matches multiple criteria, pass an object that contains both tests. This is similar to an AND (&&), but for one property. If you try to do a normal AND statement, but use the same property, twice it won't work.

db.employees.find(
    {
        salary: {
            $gte : 80,
            $lte : 165
        }
    }
);

Explain intermediate update operators

We can increase a specific value

db.employees.update(
    {
        name: 'Pilot'
    },
    {
        $inc: {
            salary: -2
        }
    }
)

Multiple a value

db.employees.update(
    {
        name: 'Pilot'
    },
    {
        $mul: {
            salary: (1/2)
        }
    }
)

Push a value onto an array

db.employees.update(
    {
        name: 'Aurora'
    },
    {
        $push: {
            loves: 'sugar'
        }
    }
)

Pop a value off an array

db.employees.update(
    {
        name: 'Aurora'
    },
    {
        $pop: {
            loves: 1
        }
    }
)

Remove a property altogether

db.employees.update(
    {
        name: 'Aurora'
    },
    {
        $unset: {
            loves: ''
        }
    }
)

Rename a field

db.employees.update(
    {
        name: 'Aurora'
    },
    {
        $rename: {
            wrong_field_name : 'correct_field_name'
        }
    }
)

For more operators, look here: http://docs.mongodb.org/manual/reference/operator/update/#update-operators

Explain upserts

Upserts will insert a value if it doesn't exist. If it does, it will update it.

Normal:

db.hits.update(
    {
        page: 'employees'
    },
    {
        $inc: {
            hits: 1
        }
    }
);
db.hits.find();

Upsert:

db.hits.update(
    {
        page: 'employees'
    },
    {
        $inc: {
            hits: 1
        }
    },
    {
        upsert:true
    }
);
db.hits.find();
db.hits.update(
    {
        page: 'employees'
    },
    {
        $inc: {
            hits: 1
        }
    },
    {
        upsert:true
    }
);
db.hits.find();

Summary

MongoDB is quite versatile and gives the developer a lot more freedom than SQL. What would easily break a SQL database - like suddenly removing or renaming a column - are totally fine in a Mongo database!