Home > Articles > Data

Choosing Design Patterns for Your Document Databases

Dan Sullivan (author of NoSQL for Mere Mortals) and James Sullivan discuss the options for modeling various design patterns in a document database system.
Like this article? We recommend

Like this article? We recommend

Document databases are a popular alternative to relational databases because they offer greater flexibility and scalability. With their distinct characteristics, document databases have led to several useful design patterns. This article provides some tips for modeling one-to-many, many-to-many, trees, and hierarchies, sharing some guidelines for choosing an appropriate pattern for various needs.

Modeling One-to-Many Using Embedded Documents

The embedded approach to modeling one-to-many relationships reduces the complexity of retrieving data, at the cost of additional storage space. With this model, multiple documents are embedded within one, in order to simplify data access and possibly improve performance.

Consider an order document for an e-commerce website. Using the one-to-many model, the order document has an ID and fields indicating the details of the order, such as payment and shipping information. The data for each item in the order, such as product name, quantity, and sales price, is stored in item documents within the order document.

Embedding the attributes of a "many" entity in a one-to-many document allows application developers to take advantage of single fetch operations that return both primary and related data. If used properly, these fetch operations improve performance by reducing latency associated with retrieving additional data blocks when the many entities are stored in a separate collection.

There are some disadvantages to embedding "many" attributes:

  • Embedded one-to-many models increase document size. Such a model must be implemented carefully to prevent performance degradation.
  • Attributes of the "many" entity that are used frequently with the parent entity should be embedded. When embedding is overused, however, data is read more often than necessary, slowing the application.

Modeling Many-to-Many Using References

Many-to-many relationships occur when no single parent entity is associated with an entity. For example, employees may work on many projects, and projects may have many employees assigned. In document databases, this type of relationship can be modeled with references or with embedded documents.

Document identifiers (references) provide an efficient way to organize information with a many-to-many model. References are essentially embedded IDs that refer to other documents; they function much like foreign keys in relational databases. As with embedding documents, using references has advantages and disadvantages:

  • Because a reference is just an ID for a separate piece of information, redundancy is minimized. Using the customer order example, if two or more customers order more than one of the same item, using a reference minimizes the need to store redundant copies of that item's data. This design keeps the documents relatively small and free of redundancy.
  • On the other hand, references sometimes force multiple read operations in order to fetch all referenced documents.

Modeling Many-to-Many Using Embedded Documents

Many-to-many models can also utilize document embedding. When implemented within the many-to-many model, this method stores multiple documents within an outer document. For example, this method may be useful when organizing the employee-to-project relationship and workflow.

As employees work on multiple projects, and projects take on multiple employees, the many-to-many architecture helps to streamline document storage. The project collection may include project documents, each containing embedded employee documents that describe the employees working on the project. Similarly, the employee collection might contain employee documents. Each employee document would have an embedded document describing each project on which that particular employee worked.

Embedded documents are useful when you need to capture point-in-time data that may change in the future. For example, if a project document contains only employee IDs of those currently working on a project, then past employees on the project will not be represented. By storing embedded employee documents along with start and end dates, you can store a history of who has worked on a project.

The one major disadvantage of the embedded document approach, much like with the one-to-many example, is the large size of documents. In general, using a many-to-many model with embedded documents works best with small to medium-sized documents and collections.

Modeling Trees

Using trees in documents databases is an efficient way to organize both reference-based and embedded-based document models. Trees are commonly used to represent "is-a" and "part-of" relationships.

For example, a product hierarchy might include the type "electronics" with a set of subtypes such as mobile, home audio, and home video equipment. These subtypes may in turn be broken down further, with mobile products including phones, tablets, and so on. An example "part-of" relationship is an automobile that has an electrical system and a transmission, and under the electrical system are the ignition and lighting systems.

If trees are of arbitrary depth, using references is a good choice. This approach will keep the size of any given document under control by preventing it from being overrun with embedded documents. At any point in the tree, you can embedded a reference to the parent node or a list of references to children nodes.

Using children references promotes top-down navigation of documents, whereas parent references promote bottom-up navigation. A combination of the two referencing methods allows for comprehensive navigation of stored documents.

Avoiding Too Much of a Good Thing

It's important to watch for adverse effects when using these patterns. For instance, look out for large arrays or significant growth in document size after adding embedded documents. Documents can grow larger than the space allocated to them, which can trigger the database to copy the data to a new location. This result takes more space than necessary and can have a significant impact on performance.

A second word of warning: Avoid fetching more data than needed, which can slow down reads and unnecessarily increase response times for your queries. If any of these symptoms occur, consider revising your data model.

Summary

The various design patterns for document databases offer different advantages and disadvantages, and rarely is one answer right for every situation. When choosing a document database pattern, always keep in mind your database's query requirements and the volume of data in your collections.

Dan Sullivan, author of NoSQL for Mere Mortals, is an enterprise architect and consultant with over 20 years of IT experience with engagements in advanced analytics, systems architecture, database design, enterprise security and business intelligence.

James Sullivan is a business technology writer with concentrations in mobile, security and database services. He is based in Portland, Oregon.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020