Indexing in a database is a technique used to speed up data lookup from tables or collections. Without indexing, it may take some time to find an entry. For instance, if a table contains thousands or more entries without indexing, finding the data typically necessitates going through each row. In indexing one or more columns can be used to generate indexes and stored in an ordered manner. Which results in quick and efficient lookup of data.
MongoDB has an index for the _id field by default. In addition to the default index, a user can also define single field indexes and multiple fields. These indexes are created using the keyword ’createIndex’.
To show all indexes in a collection use the command ‘db.collectionName.getIndexes()’
To drop an index from a collection use the command ‘db.collectionName.dropIndexes(fieldName:type)’
Types of Indexes in MongoDB
Single Field Index
To create an index on a single field in a collection, use single field index
Syntax : db.collectionName.createIndex({fieldName:1})
Example : db.salesInventory.createIndex({item:1})
In the above example the collection name is salesInventory and item is the field inside that collection. The number 1 indicates the sort order .Sorting in ascending order is denoted by 1 ,whereas -1 indicates sorting in descending order.
Compound Index
Compound indexes are indexes that contain multiple fields.
Syntax: db.collectionName. createIndex({filed1:type, field2:type, …..})
Example : db.employee. createIndex({empName:1, empDept:-1})
In this illustration, the employee collection’s files empName and empDept are indexed.
empName in ascending order and empDept in descending order.
Multikey Index
To use indexing for an array field in a collection use multikey indexing.
Syntax : db. CollectionName. createIndex({arrayName:arrayKey:type})
Example : db. examResults. createIndex({evaluationData:markScored:1})
Collection Example : examResult { id:ObjectId(“64548f497fae9e42e9013f68”),
name:Jane
class:12
evaluationData:{
{subject:”English”,markScored:”86”,maxMark:”100”},
{subject:”Science”,markScored:”92”,maxMark:”100”},
}
}
In the above example evaluationData is a collection filed in array format.
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