notes.md

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7-1: Overview Of the previous Module, Install Studio 3T, No SQL Booster

Mongoose practice json data

All methods of MongoDB work on Mongoose except insert, insertMany.

Because Mongoose validates the data through schema before saving it on the database. But insert, insertMany is used to save any kind of data in the database.

• show database → shows all databases in the compass
• use practice-mongoose → switches to database
• db.practice.find()

To increase the UX of the compass we can use studio 3t or NoSQLBooster GUI

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7-2: Explore $eq, $ne, $gt, $lt, $gte, $lte Operator

Operators are always used inside {}.

• $eq → equality
• $ne → not equal
• $gt → greater than
• $gte → greater than equal
• $lt → less than
• $lte → less than equal

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7-3: Explore $in, $nin, Nested Condition

• $in → returns only the fields that have the values provided in the array.

// syntax
{ field: { $in: [value1, value2, ... value10 ] } } 

// example
db.practice.find({ age: { $in: [18, 23] } } )

• $nin → opposite of $in
  • returns only the fields that do not have the values provided in the array.
  • or the field doesn’t exist.
• implicit and: MongoDB provides an implicit AND operation when specifying a comma-separated list of expressions.
• Nested condition:

db.practice
    .find({
        gender: "Female",
        age: { $nin: [18, 23, 33, 46, 30] }, 
        interests: { $in: ["Gaming", "Cooking"], }
    })
    .project({
        _id: 0,
        gender: 1,
        age: 1,
        interests: 1
    })

This is also an example of implicit $and. Cause we are using commas to separate the conditions.

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7-4: Explore $and, $or, Implicit vs explicit and

• $and → used to nest condition. Returns the fields that satisfy all the conditions.

.find({
        $and: [
            { gender: "Female" },
            { age: { $lt: 30 } },
            { "skills.name": "JAVASCRIPT" }
        ]
    })

• $or → opposite of $and. Returns the fields that satisfy any condition.

.find({
        $or: [
            { gender: "Female" },
            { age: { $lt: 30 } },
						{ "skills.name": { $in: ["JAVASCRIPT", "PYTHON"] } }
        ]
    })

Implicit vs Explicit and

Implicit can’t be used for the same field. Explicit and is used for it.

// Implicit `and` gives bug
find({
    age: { $gt: 15 },
    age: { $ne: 18 },
})

// Explicit `and` corrects it
find({
    $and: [
        { age: { $ne: 18 } },
        { age: { $gt: 15 } }
    ]
})

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7-5: Explore $exists, $type, $size operator

• $exists → checks if a field exists in a document.
• $type → checks the data type of a field.
• $size → checks the length of the array. Size means no of elements on an array.

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7-6: Explore $all, $elemMatch Operator Part-1

Array query operators

• $all → run on a property with an array value. Returns all the docs that have all the values passed on to the operator { <field>: { $all: [ <value1>, <value2> ... ] } }

find({
    interests: { $all: ["Gaming", "Cooking", "Reading"] }
})

// using `$and` 
find({
    $and: [
        { interests: "Gaming" },
        { interests: "Reading" },
        { interests: "Cooking" }
    ]
})

Though $and can also do the work, using $all is more convenient and easier.

Query with specifying the index of an array 👇

// finds all the arrays where the first element is "Gardening"
find({
    "interests.0": "Gardening"
})

• $elemMatch → finds documents that have an array field with at least one element that meets a specific condition. It helps you search for documents where multiple conditions must be met by the same element in an array.

// runs on an array of objects.
// returns the documents that have {name: "JAVA", level: "Intermediate"} this element
// in the array
find({
    skills: {
        $elemMatch: {
            name: "JAVA",
            level: "Intermidiate"
        }
    }
})

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7-7: Explore $set, $addToSet, $push operator (Update)

• $set → replaces the value of a field with the given value

  • used when needed to add a new field in the document
  • used to change the value of a field
  • thumb rule: use it for only primitive types. Cause $set replaces the whole value, it’s a field update operator.

• $addToSet → adds a value to an array if it is not present.

  use it with $each modifier to add each value to an array. It will not add the values that are already present in the array

• $push → pushes a value to an array. It can cause duplication. It can also be used with $each for the same purpose, to push multiple values to an array.

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7-8: Explore $unset, $pop, $pull, $pullALL (Delete)

• $unset → delete a field.
• $pop → removes first(1)/last(-1) element of array.
• $pull → removes single or multiple specific values from an array.
• $pullAll → removes all the elements that match the specific values

{ $pullAll: { <field1>: [ <value1>, <value2> ... ], ... } }

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7-9: Explore deleteOne, deleteMany, dropCollection, createCollection

• deleteOne
• deleteMany
• dropCollection
• createCollection

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7-10: Explore $inc, $min, How to explore documents

• $inc → increments the field by a specific value
• $min → increments the field by a specific value, if the specified value is less than the current field value
• $rename → updates the key of an existing field.