Open up any document in a MongoDB database and you'll notice an _id field:
In fact, the ObjectId/_id is the only field that exists across every MongoDB document. In today's blog, we'll explore what it is and why it's important to your MongoDB database.
You've probably heard that column indexing is a great way to optimize query performance by minimizing the number of disk accesses required by the query. MongoDB has a specific application of field indexing called Covered Queries, where all of a query's columns are indexed. Covered Queries are very fast because MongoDB doesn't have to examine any documents apart from the indexed ones. In today's blog, we'll be learning how to use Covered Queries to query data faster.
If you've ever tried to locate a specific column in a large database, I'm sure that you'd agree that it can be a painstaking task. You can glean a lot of information about the DB structure from the information_schema schema. It has a list of all tables and all fields that are in a table. You can then run queries using the information that you have gotten from this table. The specific tables involved are SCHEMATA, TABLES and COLUMNS. There are foreign keys such that you can build up exactly how the tables are created in a schema.
In last week's blog, we explored the pros and cons of document relationship modeling via Embedded and Referenced approaches in MongoDB. We then gained some valuable experience with each by creating both an Embedded and Referenced relationship. Today, we'll learn how to create DBRefs in MongoDB.
As the name implies, Relational Databases (RDBMSes) maintain relationships between the tables to organize the data together in meaningful ways. Document databases such as MongoDB are sometimes called "schema-less" due to the fact that they don't really enforce relationships like RDBMSes do. However, while document databases don't require the same predefined structure as a relational database, that doesn't mean that they don't support it. In fact, MongoDB allows relationships between documents to be modeled via Embedded and Referenced approaches. In today's blog, we'll give each a try using Navicat for MongoDB.
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