Select $unwind and then fill in the field you want, prefixed with $. If you go into Compass to the collection you want and go to the aggregation tab, you can unwind and group as such: Example: db.pets.distinct ( 'type' ) Result: 'Bat', 'Cat', 'Dog' These three values are the distinct values for the type field in the above documents. The MongoDB _id field is fundamental to every collection in MongoDB, and, by default, it has some useful properties users can take advantage of when familiar with how _id is generated.Here's a way that I've been using in Compass. In MongoDB, the db.collection.distinct () method finds the distinct values for a specified field across a single collection or view and returns the results in an array.
The syntax is as follows db.yourCollectionName. Understanding the field's default behavior and the advantages and pitfalls associated with it can be useful for managing your collections as well as understanding when to override it. You can use distinct () method in MongoDB to get distinct record values. What Is MongoDB ObjectID?As MongoDB documentation explains, "ObjectIds are small, likely unique, fast to generate, and ordered." The _id field is a 12-byte Field of BSON type made up of several 2-4 byte chains and is the unique identifier/naming convention MongoDB uses across all its content. Each chain represents and designates a specific aspect of the document's identity. How Does MongoDB ObjectID Work?Architecturally, by default the _id field is an ObjectID, one of MongoDB's BSON types. If you use the unique constraint on a compound index, then MongoDB will enforce uniqueness on the combination of the index key values.
#MONGODB COMPASS UNIQUE VALUES FULL#
The following values make up the full 12-byte combination of every _ID ( quoted from MongoDB's documentation): The ObjectID is the primary key for the stored document and is automatically generated when creating a new document in a collection.
_id is the primary key on elements in a collection with it, records can be differentiated by default.These are also a few _id field principal characteristics you should know about: a 2-byte process id, and a 3-byte counter, starting with a random value."."a 4-byte value representing the seconds since the Unix epoch. Append 'length' to the end of the query to count the number of rows returned. The first argument for 'distinct' is the field for which to aggregate distinct values, the second is the conditional statement that specifies which rows to select. Users can also override _id to something other than an ObjectID data type, if desired.Lookups specifying refer to the _id index as their guide. To count the unique values, use 'distinct ()' rather than 'find ()', and 'length' rather than 'count ()'.
Is MongoDB ObjectID Unique? According to MongoDB, ObjectID can be considered globally unique. The first nine bytes in a MongoDB _ID guarantee its uniqueness across machines and processes, in relation to a single second the last three bytes provide uniqueness within a single second in a single process.Īre There Any Fields All Documents in MongoDB Must Have? All documents in MongoDB must have a populated _id field. If a document hasn’t been assigned an _id value, MongoDB will automatically generate one. Important MongoDB Commands for ObjectIDThanks to the universal, required nature of the _id field, there are several actions available to users to simplify your organization and handling of documents. The distinct () Method In MongoDB, the db.collection.distinct () method finds the distinct values for a specified field across a single collection or view and returns the results in an array.
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