Documents
Overview
Document Structure
In Couchbase Lite the term 'document' refers to an entry in the database. You can compare it to a record, or a row in a table.
Each document has an ID or unique identifier. This ID is similar to a primary key in other databases.
You can specify the ID programmatically. If you omit it, it will be automatically generated as a UUID.
Couchbase documents are assigned to a Collection. The ID of a document must be unique within the Collection it is written to. You cannot change it after you have written the document. |
The document also has a value which contains the actual application data. This value is stored as a dictionary of key-value (k-v) pairs. The values can be made of up several different Data Types such as numbers, strings, arrays, and nested objects.
Data Encoding
The document body is stored in an internal, efficient, binary form called Fleece. This internal form can be easily converted into a manageable native dictionary format for manipulation in applications.
Fleece data is stored in the smallest format that will hold the value whilst maintaining the integrity of the value.
Data Types
The Document
class offers a set of property accessors for various scalar types, such as:
-
Boolean
-
Date
-
Double
-
Float
-
Int
-
Long
-
String
These accessors take care of converting to/from JSON encoding, and make sure you get the type you expect.
In addition to these basic data types Couchbase Lite provides for the following:
- Dictionary
-
represents a read-only key-value pair collection
- MutableDictionary
-
represents a writeable key-value pair collection
- Array
-
represents a readonly ordered collection of objects
- MutableArray
-
represents a writeable collection of objects
- Blob
-
represents an arbitrary piece of binary data
JSON
Couchbase Lite also provides for the direct handling of JSON data implemented in most cases by the provision of a toJSON()
method on appropriate API classes (for example, on MutableDocument, Dictionary, Blob and Array) — see Working with JSON Data.
Constructing a Document
An individual document often represents a single instance of an object in application code.
You can consider a document as the equivalent of a 'row' in a relational table, with each of the document’s attributes being equivalent to a 'column'.
Documents can contain nested structures. This allows developers to express many-to-many relationships without requiring a reference or join table, and is naturally expressive of hierarchical data.
Most apps will work with one or more documents, persisting them to a local database and optionally syncing them, either centrally or to the cloud.
In this section we provide an example of how you might create a hotel
document, which provides basic contact details and price data.
hotel: {
type: string (value = `hotel`)
name: string
address: dictionary {
street: string
city: string
state: string
country: string
code: string
}
phones: array
rate: float
}
Open a Database
First open your database. If the database does not already exist, Couchbase Lite will create it for you.
Couchbase documents are assigned to a Collection.
All the CRUD examples in this document operate on a collection
object (here, the Default Collection).
// Get the database (and create it if it doesn’t exist).
let database = try Database(name: "hoteldb")
let collection = try database.createCollection(name: "hotel")
See Databases for more information
Create a Document
Now create a new document to hold your application’s data.
Use the mutable form, so that you can add data to the document.
// Create your new document
// The 'var' indicates this document instance can be mutated
var mutableDoc = MutableDocument(id: "doc1")
For more on using Documents, see Document Initializers and Mutability.
Create a Dictionary
Now create a mutable dictionary (address
).
Each element of the dictionary value will be directly accessible via its own key.
// Create and populate mutable dictionary
// Create a new mutable dictionary and populate some keys/values
var address = MutableDictionaryObject()
address.setString("1 Main st.", forKey: "street")
address.setString("San Francisco", forKey: "city")
address.setString("CA", forKey: "state")
address.setString("USA", forKey: "country")
address.setString("90210", forKey: "code")
Learn more about Using Dictionaries.
Create an Array
Since the hotel may have multiple contact numbers, provide a field (phones
) as a mutable array.
// Create and populate mutable array
var phones = MutableArrayObject()
phones.addString("650-000-0000")
phones.addString("650-000-0001")
Learn more about Using Arrays
Populate a Document
Now add your data to the mutable document created earlier. Each data item is stored as a key-value pair.
// Initialize and populate the document
// Add document type and hotel name as string
mutableDoc.setString("hotel", forKey:"type")
mutableDoc.setString("Hotel Java Mo", forKey:"name")
// Add average room rate (float)
mutableDoc.setFloat(121.75, forKey:"room_rate")
// Add address (dictionary)
mutableDoc.setDictionary(address, forKey: "address")
// Add phone numbers(array)
mutableDoc.setArray(phones, forKey:"phones")
Couchbase recommend using a type attribute to define each logical document type.
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Working with Data
Checking a Document’s Properties
To check whether a given property exists in the document, use the Document.Contains(key:) method.
If you try to access a property which doesn’t exist in the document, the call will return the default value for that getter method (0 for Document.int() 0.0 for Document.float() etc.).
Date accessors
Couchbase Lite offers Date accessors as a convenience. Dates are a common data type, but JSON doesn’t natively support them, so the convention is to store them as strings in ISO-8601 format.
This example sets the date on the createdAt
property and reads it back using the Document.date() accessor method.
let mutableDoc = MutableDocument(id: "xyz")
mutableDoc.setValue(Date(), forKey: "createdAt")
guard let doc = try collection.document(id: "xyz") else { return }
let date = doc.date(forKey: "createdAt")
Using Dictionaries
// NOTE: No error handling, for brevity (see getting started)
guard let doc = try collection.document(id:"doc1") else { return }
// Getting a dictionary from the document's properties
guard let dict = doc.dictionary(forKey: "address") else { return }
// Access a value with a key from the dictionary
guard let street = dict.string(forKey: "street") else { return }
// Iterate dictionary
for key in dict.keys {
print("Key \(key) = \(dict.value(forKey:key) ?? "--")")
}
// Create a mutable copy
let mutableDict = dict.toMutable()
// Create a new mutable dictionary and populate some keys/values
let mutableDict = MutableDictionaryObject()
mutableDict.setString("1 Main st.", forKey: "street")
mutableDict.setString("San Francisco", forKey: "city")
// Add the dictionary to a document's properties and save the document
let mutableDoc = MutableDocument(id: "doc1")
mutableDoc.setDictionary(mutableDict, forKey: "address")
try! collection.save(document:mutableDoc)
Using Arrays
guard let doc = try collection.document(id:"doc1") else { return }
// Getting a phones array from the document's properties
guard let array = doc.array(forKey: "phones") else { return }
// Access an array element by index
if array.count >= 0, let val = array.string(at: 0) {
phone = val
}
// Iterate dictionary
for (index, element) in array.enumerated() {
print("Index \(index) = \(element)")
}
// Create a mutable copy
let mutableArray = array.toMutable()
// Create a new mutable array and populate data into the array
var mutableArray = MutableArrayObject()
mutableArray.addString("650-000-0000")
mutableArray.addString("650-000-0001")
// Set the array to document's properties and save the document
let mutableDoc = MutableDocument(id: "doc1")
mutableDoc.setArray(mutableArray, forKey:"phones")
try collection.save(document:mutableDoc)
Using Blobs
For more on working with blobs, see Blobs
Document Initializers
You can use the following methods/initializers:
-
Use the MutableDocument() initializer to create a new document where the document ID is randomly generated by the database.
-
Use the MutableDocument(String id) initializer to create a new document with a specific ID.
-
Use the {url-api-method-collection-getdocument} method to get a document. If the document doesn’t exist in the collection, the method will return
null
. You can use this behavior to check if a document with a given ID already exists in the collection.
The following code example creates a document and persists it to the database.
let doc = MutableDocument()
.setString("task", forKey: "type")
.setString("todo", forKey: "owner")
.setDate(Date(), forKey: "createdAt")
try collection.save(document: doc)
Mutability
By default, a document is immutable when it is read from the database. Use the Document.toMutable() to create an updatable instance of the document.
Changes to the document are persisted to the database when the save
method is called.
guard let doc = try collection.document(id: "xyz") else { return }
let mutableDocument = doc.toMutable()
mutableDocument.setString("apples", forKey: "name")
try collection.save(document: mutableDocument)
Any user change to the value of reserved keys (_id , _rev or _deleted ) will be detected when a document is saved and will result in an exception (Error Code 5 — CorruptRevisionData ) — see also Document Constraints.
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Document Conversion
You can convert a Document
to a plain dictionary type and/or to a JSON string.
This can often be useful to pass the document contents as a plain object to another method.
guard let doc = try collection.document(id: "xyz") else { return }
print(doc.toDictionary())
guard let doc = try collection.document(id: "xyz") else { return }
print(doc.toJSON())
Batch operations
If you’re making multiple changes to a database at once, it’s faster to group them together. The following example persists a few documents in batch.
do {
try database.inBatch {
for i in 0...10 {
let doc = MutableDocument()
doc.setValue("user", forKey: "type")
doc.setValue("user \(i)", forKey: "name")
doc.setBoolean(false, forKey: "admin")
try collection.save(document: doc)
print("saved user document \(doc.string(forKey: "name")!)")
}
}
} catch let error {
print(error.localizedDescription)
}
At the local level this operation is still transactional: no other Database
instances, including ones managed by the replicator can make changes during the execution of the block, and other instances will not see partial changes.
But Couchbase Mobile is a distributed system, and due to the way replication works, there’s no guarantee that Sync Gateway or other devices will receive your changes all at once.
Document change events
You can register for document changes.
The following example registers for changes to the document with ID user.john
and prints the verified_account
property when a change is detected.
weak var wCollection = collection
let token = collection.addDocumentChangeListener(id: "user.john") { (change) in
if let doc = try? wCollection?.document(id: change.documentID) {
print("Status :: \(doc?.string(forKey: "verified_account") ?? "--")")
}
}
Document Expiration
Document expiration allows users to set the expiration date for a document. When the document expires, it is purged from the database. The purge is not replicated to Sync Gateway.
This example sets the TTL for a document to 1 day from the current time.
// Purge the document one day from now
let ttl = Calendar.current.date(byAdding: .day, value: 1, to: Date())
try collection.setDocumentExpiration(id: "doc123", expiration: ttl)
// Reset expiration
try collection.setDocumentExpiration(id: "doc1", expiration: nil)
// Query documents that will be expired in less than five minutes
let fiveMinutesFromNow = Date(timeIntervalSinceNow: 60 * 5).timeIntervalSince1970
let query = QueryBuilder
.select(SelectResult.expression(Meta.id))
.from(DataSource.collection(collection))
.where(
Meta.expiration.lessThan(
Expression.double(fiveMinutesFromNow)
)
)
You can set expiration for a whole Collection
Document Constraints
Couchbase Lite APIs do not explicitly disallow the use of attributes with the underscore prefix at the top level of document. This is to facilitate the creation of documents for use either in local only mode where documents are not synced, or when used exclusively in peer-to-peer sync.
"_id", :"_rev" and "_sequence" are reserved keywords and must not be used as top-level attributes — see Example 12. |
Users are cautioned that any attempt to sync such documents to Sync Gateway will result in an error. To be future proof, you are advised to avoid creating such documents. Use of these attributes for user-level data may result in undefined system behavior.
For more guidance — see: Sync Gateway - data modeling guidelines
Working with JSON Data
- In this section
-
Arrays | Blobs | Dictionaries | Documents | Query Results as JSON
The toJSON()
typed-accessor means you can easily work with JSON data, native and Couchbase Lite objects.
Arrays
Convert an ArrayObject
to and from JSON using the toJSON()
and toArray
methods — see Example 4.
Additionally you can:
-
Initialize a 'MutableArrayObject' using data supplied as a JSON string. This is done using the
init(json)
constructor — see: Example 4 -
Convert an
ArrayFragment
object to a JSON String -
Set data with a JSON string using
setJSON()
if let doc = try collection.document(id: "1000") {
guard let array = doc.array(forKey: "list") else {
return
}
let json = array.toJSON()
print(json)
}
Blobs
Convert a Blob
to JSON using the toJSON
method — see Example 14.
You can use isBlob()
to check whether a given dictionary object is a blob or not — see Example 14.
Note that the blob object must first be saved to the database (generating the required metadata) before you can use the toJSON
method.
// Get a document
if let doc = try collection.document(id: "1000") {
guard let blob = doc.blob(forKey: "avatar") else {
return
}
let json = blob.toJSON()
print(json)
}
See also: Blobs
Dictionaries
Convert a DictionaryObject
to and from JSON using the toJSON
and toDictionary
methods — see Example 15.
Additionally you can:
-
Initialize a 'MutableDictionaryObject' using data supplied as a JSON string. This is done using the
init(json)
constructor-- see: Example 15 -
Set data with a JSON string using
setJSON()
if let doc = try collection.document(id: "1000") {
guard let dictionary = doc.dictionary(forKey: "dictionary") else {
return
}
let json = dictionary.toJSON()
print(json)
}
Documents
Convert a Document
to and from JSON strings using the toJSON()
and setJSON()
methods — see Example 16.
Additionally you can:
-
Initialize a 'MutableDocument' using data supplied as a JSON string. This is done using the
init(json)
orinit(id: json:)
constructor — see: Example 16 -
Set data with a JSON string using
setJSON()
let collection = try self.database.createCollection(name: "hotel")
let query = QueryBuilder
.select(SelectResult.expression(Meta.id).as("metaId"))
.from(DataSource.collection(collection))
if let doc = try collection.document(id: "doc-id") {
let json = doc.toJSON()
print(json)
}
Query Results as JSON
Convert a Query Result
to JSON using its toJSON()
accessor method.
Use result.toJSON() to transform your result string into a JSON string, which can easily be serialized or used as required in your application. See <
// In this example the Hotel class is defined using Codable
//
// class Hotel : Codable {
// var id : String = "undefined"
// var type : String = "hotel"
// var name : String = "undefined"
// var city : String = "undefined"
// var country : String = "undefined"
// var description : String? = ""
// var text : String? = ""
// ... other class content
// }
let results = try query.execute()
for row in results {
// get the result into a JSON String
let jsonString = row.toJSON()
let thisJsonObj:Dictionary =
try (JSONSerialization.jsonObject(
with: jsonString.data(using: .utf8)!,
options: .allowFragments)
as? [String: Any])!
// Use Json Object to populate Native object
// Use Codable class to unpack JSON data to native object
var this_hotel: Hotel = try JSONDecoder().decode(Hotel.self, from: jsonString.data(using: .utf8)!) (1)
// ALTERNATIVELY unpack in steps
this_hotel.id = thisJsonObj["id"] as! String
this_hotel.name = thisJsonObj["name"] as? String
this_hotel.type = thisJsonObj["type"] as? String
this_hotel.city = thisJsonObj["city"] as? String
hotels[this_hotel.id] = this_hotel
} // end for
If your query selects ALL then the JSON format will be:
{
database-name: {
key1: "value1",
keyx: "valuex"
}
}
If your query selects a sub-set of available properties then the JSON format will be:
{
key1: "value1",
keyx: "valuex"
}