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Table of Contents > Modules and Tags > Channel Module > Relationships

Relating Entries to Other Entries

Creating Data Relationships for Increased Power

ExpressionEngine allows you to create relationships between entries in different channels, or between channel entries.

Why would you relate entries to other entries?

Here is an example to illustrate why someone would want to create relationships between entries.

The Night Club Owner

Imagine that you run a night club in which different musical artists perform nightly. To help promote your club you decide to create an ExpressionEngine channel to display information about each night's events.

Each day you submit a new entry with information about a particular night's performances. You also include detailed information about each performer (names, bio, discography, etc.), but since many of the performers appear regularly at your club, over time you end up with a lot of duplicated information in your entries. And if a piece of information about a performer changes you have to updated it in every entry that mentions them. Before long you realize that this is not very efficient.

If only you could maintain a second channel in which you store only information about each performer, and then connect it somehow to the main channel so that you would never have to duplicate information. Guess what? You can with relationships.

In the above scenario, your primary channel (let's call the channel Events) would contain only information that is unique about a particular night, like the date, time, any special pricing, etc., and the second channel (let's call the channel Performers) would contain only information about each performer. You would then dynamically pull information from each performer into the appropriate Events channel. To your site visitors the information appears just like a normal channel entry, but internally, ExpressionEngine is pulling information from one entry and showing it within another.

The following graphic illustrates the concept. The "events" channel on the left is showing information from the "performers" channel on the right. Only a relationship exists between the entries. The data itself is never duplicated.

Each channel entry can be related to one or more entries from other Channels.

Setting Up A Relationship

There are two steps to setting up a relationship, described in detail next:

1. Create the relationship between a channel and another.
2. Add "related entry" tags to your Templates so the related data can be shown.

Once your relationship is set up, whenever you access the PUBLISH page to submit new content you'll see a drop-down menu showing the titles of all the entries in the related channel. Choose a particular entry from the list and voila... the entries will be related.

1. Create the Relationship

A relationship is defined in the Custom Field Manager, located in your Control Panel here:

Admin > Channel Management > Custom Channel Fields

Custom fields can be one of several types, including Relationship types. When you set up a custom field as a relationship type you'll be asked to choose which channel to associate it with. Once that association is set you'll see a drop-down menu in the PUBLISH page showing the titles of all the entries in the related channel.

2. Add Related Entry Tags to your Template

To show a related entry, you will use the following tags:

{related_entries id="field_name"}

{/related_entries}

Note: The id parameter must contain the Field Name of the custom field that contains the relationship. For example, if your custom field is called performers you'll use this:

{related_entries id="performers"}

{/related_entries}

Important: The above tags must be placed inside your {exp:channel:entries} tag.

Here is an example showing the related entries tags inside your channel entry tags:

{exp:channel:entries channel="news" limit="15"}

<h3>{title}</h3>

{body}

{related_entries id="performers"}
 <h2>{title}</h2>
 {body}
{/related_entries}

Submitted on: {entry_date format='%M %d, %Y'}

{/exp:channel:entries}

{if no_related_entries} Conditional

The {if no_related_entries} conditional allows you specify certain content to be displayed when an entry does not have a related entry for the field specified.

{exp:channel:entries channel="news" limit="15"}

<h3>{title}</h3>

{body}

{related_entries id="performers"}
 {if no_related_entries}
  <h2>No Performer Information Available</h2>
 {/if}
 <h2>{title}</h2>
 {body}
{/related_entries}

Submitted on: {entry_date format='%M %d, %Y'}

{/exp:channel:entries}

What Type of Related Data can be Displayed?

Nearly anything that is available in the channel entries tags can be shown as related data.

• {exp:channel:entries}

Examples:

Channel:  To relate a channel entry to another you'll do something similar to this:

{exp:channel:entries channel="news" limit="15"}

<h3>{title}</h3>

{body}

{related_entries id="channel"}

   {date_heading}
   <h3 class="date">{entry_date format=' %l, %F %d, %Y '}</h3>
   {/date_heading}

   <h2 class="title">{title}</h2>
   {summary}

   <div class="posted">Posted by <a href="{profile_path='member/index'}">{author}</a> on {entry_date format='%m/%d'}

   {categories}
   <a href="{path='SITE_INDEX'}">{category_name}</a>
   {/categories}

{/related_entries}

Submitted on: {entry_date format='%M %d, %Y'}

{/exp:channel:entries}

As indicated above: Do not place the opening/closing entry tags within the related tags. ONLY put the variables and HTML you'd like to appear.

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