MongoEngine – Dynamic Schema
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One of the advantages of MongoDB database is that it supports dynamic schema. To create a class that supports dynamic schema, subclass it from DynamicDocument base class. Following is the Student class with dynamic schema −
>>> class student(DynamicDocument): ... name=StringField()
The first step is to add first Document as before.
>>> s1=student()
>>> s1.name="Tara"
>>> connect(''mydb'')
>>> s1.save()
Now add another attribute to second document and save.
>>> s2=student() >>> setattr(s2,''age'',20) >>> s2.name=''Lara'' >>> s2.save()
In the database, student collection will show two documents with dynamic schema.
The meta dictionary of document class can use a Capped Collection by specifying max_documents and max_size.
max_documents − The maximum number of documents that is allowed to be stored in the collection.
max_size − The maximum size of the collection in bytes. max_size is rounded up to the next multiple of 256 by MongoDB internally and mongoengine before.
If max_size is not specified and max_documents is, max_size defaults to 10485760 bytes (10MB).
Other parameters of Document class are listed below −
| objects | A QuerySet object that is created lazily on access. |
| cascade_save() | Recursively save any references and generic references on the document. |
| clean() | Hook for doing document level data cleaning before validation is run. |
| create_index() | Creates the given indexes if required. |
| drop_collection() | Drops the entire collection associated with this Document type from the database. |
| from_json() | Converts json data to a Document instance. |
| modify() | Perform an atomic update of the document in the database and reload the document object using updated version. |
| pk | Get the primary key. |
| save() | Save the Document to the database. If the document already exists, it will be updated, otherwise it will be created. Returns the saved object instance. |
| delete() | Delete current document from database. |
| insert() | Performs bulk insert operation. |
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