Indexes are a crucial part of database performance optimization. Orionjs provides a clean, declarative way to define and manage MongoDB indexes.

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Defining Indexes

Indexes are defined as part of the collection configuration: 
import {Repository} from '@orion-js/services'
import {createCollection, typedId} from '@orion-js/mongodb'
import {schemaWithName, InferSchemaType} from '@orion-js/schema'

const UserSchema = schemaWithName('UserSchema', {
  _id: {type: typedId('user')},
  email: {type: String},
  firstName: {type: String},
  lastName: {type: String},
  createdAt: {type: Date}
})

type UserType = InferSchemaType<typeof UserSchema>

@Repository()
export class UserRepository {
  users = createCollection({
    name: 'users',
    schema: UserSchema,
    indexes: [
      {
        keys: {email: 1},
        options: {unique: true}
      },
      {
        keys: {createdAt: -1}
      },
      {
        keys: {firstName: 1, lastName: 1}
      }
    ]
  })
  
  // Repository methods...
}

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Index Types

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Single Field Index

{
  keys: {fieldName: 1}  // 1 for ascending, -1 for descending
}

​
Compound Index

{
  keys: {
    firstName: 1,
    lastName: 1
  }
}

​
Unique Index

{
  keys: {email: 1},
  options: {unique: true}
}

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TTL Index (Time-To-Live)

{
  keys: {createdAt: 1},
  options: {
    expireAfterSeconds: 86400  // Documents will be deleted after 24 hours
  }
}

​
Text Index

{
  keys: {description: 'text', title: 'text'},
  options: {
    weights: {
      title: 10,      // Title fields are more important
      description: 5  // Description fields are less important
    },
    name: 'TextIndex' // Custom name for the index
  }
}

​
Geospatial Index

{
  keys: {location: '2dsphere'}
}

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Index Options

The options object can include the following properties: 
{
  unique: boolean,        // Whether the index should be unique
  sparse: boolean,        // Only index documents that have the indexed field
  expireAfterSeconds: number, // Time to live for indexed documents
  name: string,           // Custom name for the index
  background: boolean,    // Create the index in the background
  partialFilterExpression: object, // Filter expression for partial indexes
  collation: object,      // Language-specific collation rules
  // ... other MongoDB index options
}

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Partial Indexes

Partial indexes only index documents that meet a specified filter expression: 
{
  keys: {email: 1},
  options: {
    unique: true,
    partialFilterExpression: {
      status: 'active'  // Only index active users' emails
    }
  }
}