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Use Displays To Summarize Relational Items ​

Displays provide a meaningful way for users to consume data. This guide will show you how to create a display that queries another table and returns the SUM or COUNT of a column.

In a table, a new field called 'Test Junction' is shown. The values are '5 items' and '2 items'.

Install Dependencies ​

Open a console to your preferred working directory and initialize a new extension, which will create the boilerplate code for your display.

shell
npx create-directus-extension@latest
npx create-directus-extension@latest

A list of options will appear (choose display), and type a name for your extension (for example, directus-display-sum-count). For this guide, select JavaScript.

Now the boilerplate has been created, open the directory in your code editor.

Specify Configuration ​

Displays have 2 parts, the index.js configuration file, and the display.vue view. The first part allows you to configure options and the appearance when selecting the display for a field.

Open the index.js file and update the existing information relevant to this display. Since you are working with relational fields, you need to change types value and add localTypes as well. This will ensure this display will only be available for relational fields.

js
import DisplayComponent from './display.vue';
import { useStores } from '@directus/extensions-sdk';

export default {
	id: 'directus-display-count-sum',
	name: 'Count or Sum a Column',
	icon: '123',
	description: 'Count the related records or display the sum of the select column',
	component: DisplayComponent,
	options: null,
	types: ['alias', 'string', 'uuid', 'integer', 'bigInteger', 'json'],
	localTypes: ['m2m', 'm2o', 'o2m', 'translations', 'm2a', 'file', 'files'],
	fields: (options) => {
		return [];
	},
};
import DisplayComponent from './display.vue';
import { useStores } from '@directus/extensions-sdk';

export default {
	id: 'directus-display-count-sum',
	name: 'Count or Sum a Column',
	icon: '123',
	description: 'Count the related records or display the sum of the select column',
	component: DisplayComponent,
	options: null,
	types: ['alias', 'string', 'uuid', 'integer', 'bigInteger', 'json'],
	localTypes: ['m2m', 'm2o', 'o2m', 'translations', 'm2a', 'file', 'files'],
	fields: (options) => {
		return [];
	},
};

Make sure the id is unique between all extensions including ones created by 3rd parties - a good practice is to include a professional prefix. You can choose an icon from the library here.

With the information above, the display will appear in the list like this:

A new display option is shown - Related Values.

Currently the options object is null. To provide the option to include months, update the options object with the following code:

js
options: null, 
options: ({ editing, relations }) => { 
	return []; 
}, 
options: null, 
options: ({ editing, relations }) => { 
	return []; 
},

Before the options return value, add the following constants to retrieve the related collection and the field store and determine if the related collection uses a junction table:

js
const relatedCollection =
	relations.o2m?.meta.junction_field != null ? relations.m2o?.related_collection : relations.o2m?.collection;

const junction_table = relations.o2m?.meta.junction_field != null ? relations.o2m?.collection : null;
const { useFieldsStore } = useStores();
const fieldsStore = useFieldsStore();
const relatedCollection =
	relations.o2m?.meta.junction_field != null ? relations.m2o?.related_collection : relations.o2m?.collection;

const junction_table = relations.o2m?.meta.junction_field != null ? relations.o2m?.collection : null;
const { useFieldsStore } = useStores();
const fieldsStore = useFieldsStore();

After the constants, add an if statement to disable the field selection dropdown while the relational field is still being created. The variable called editing was included in the function which will equal + during this state. Use the presentation-notice interface to display a message while this display is unavailable.

js
if (editing === '+') {
	const fieldSelection = {
		interface: 'presentation-notice',
		options: {
			text: 'Please complete the field before attempting to configure the display.',
		},
		width: 'full',
	};
} else {
}
if (editing === '+') {
	const fieldSelection = {
		interface: 'presentation-notice',
		options: {
			text: 'Please complete the field before attempting to configure the display.',
		},
		width: 'full',
	};
} else {
}

In the else block, use the fieldStore to fetch all the fields from the related collection into the field_choices array, then create a selection dropdown interface with the choices set to field_choices:

js
if (editing === '+') {
} else {
	const fields = fieldsStore.getFieldsForCollection(relatedCollection); 
	const field_choices = []; 

	fields.forEach((field) => { 
		field_choices.push({ 
			text: field.meta.field, 
			value: junction_table ? `${relations.o2m.meta.junction_field}.${field.meta.field}` : field.meta.field, ,
		}); 
	}); 

	const fieldSelection = { 
		interface: 'select-dropdown', 
		options: { 
			choices: field_choices, 
		}, 
		width: 'full', 
	}; 
}
if (editing === '+') {
} else {
	const fields = fieldsStore.getFieldsForCollection(relatedCollection); 
	const field_choices = []; 

	fields.forEach((field) => { 
		field_choices.push({ 
			text: field.meta.field, 
			value: junction_table ? `${relations.o2m.meta.junction_field}.${field.meta.field}` : field.meta.field, ,
		}); 
	}); 

	const fieldSelection = { 
		interface: 'select-dropdown', 
		options: { 
			choices: field_choices, 
		}, 
		width: 'full', 
	}; 
}

Inside the returned array, output all of the options to use with this display. For the field called column, set meta to fieldSelection. The rest can be added as normal.

js
return [
	{
		field: 'column',
		name: 'Choose a column',
		meta: fieldSelection,
	},
	{
		field: 'sum',
		type: 'boolean',
		name: 'Calculate Sum',
		meta: {
			interface: 'boolean',
			options: {
				label: 'Yes',
			},
			width: 'half',
		},
	},
	{
		field: 'prefix',
		type: 'string',
		name: 'Prefix',
		meta: {
			interface: 'input',
			options: {
				font: 'monospace',
			},
			width: 'half',
		},
	},
	{
		field: 'suffix',
		type: 'string',
		name: 'Suffix',
		meta: {
			interface: 'input',
			options: {
				font: 'monospace',
			},
			width: 'half',
		},
	},
];
return [
	{
		field: 'column',
		name: 'Choose a column',
		meta: fieldSelection,
	},
	{
		field: 'sum',
		type: 'boolean',
		name: 'Calculate Sum',
		meta: {
			interface: 'boolean',
			options: {
				label: 'Yes',
			},
			width: 'half',
		},
	},
	{
		field: 'prefix',
		type: 'string',
		name: 'Prefix',
		meta: {
			interface: 'input',
			options: {
				font: 'monospace',
			},
			width: 'half',
		},
	},
	{
		field: 'suffix',
		type: 'string',
		name: 'Suffix',
		meta: {
			interface: 'input',
			options: {
				font: 'monospace',
			},
			width: 'half',
		},
	},
];

Now that options are set up, use the options.column to set the scope for the fields at the very bottom of this script. This section determines what fields are included in the props.value. For example, if you set this to ['*'], all the fields for the related collection will be included. For best performance, set this to the field chosen in the options.

js
fields: (options) => {
    return [];  
    return [options.column] 
},
fields: (options) => {
    return [];  
    return [options.column] 
},

Note, displays will fetch related collection values for each row on the page. Fetching more that you need will impact the performance of Directus.

Here is a preview of how this appears in Directus:

New display options showing a select field for column, a checkbox for calculate sum, and text fields for prefix and suffix.

Build the View ​

The display.vue file contains the barebones code required for a display to work. The value is imported in the props section, then output in the template:

vue
<template>
	<div>Value: {{ value }}</div>
</template>

<script>
export default {
	props: {
		value: {
			type: String,
			default: null,
		},
	},
};
</script>
<template>
	<div>Value: {{ value }}</div>
</template>

<script>
export default {
	props: {
		value: {
			type: String,
			default: null,
		},
	},
};
</script>

Before the export, import the vue ref object:

js
import { ref } from 'vue';
import { ref } from 'vue';

Import the new display options in the props object:

js
props: {
	value: {
		type: String,
		default: null,
	},
	column: { 
		type: String, 
		default: null, 
	}, 
	sum: { 
		type: Boolean, 
		default: false, 
	}, 
	prefix: { 
		type: String, 
		default: null, 
	}, 
	suffix: { 
		type: String, 
		default: null, 
	}, 
},
props: {
	value: {
		type: String,
		default: null,
	},
	column: { 
		type: String, 
		default: null, 
	}, 
	sum: { 
		type: Boolean, 
		default: false, 
	}, 
	prefix: { 
		type: String, 
		default: null, 
	}, 
	suffix: { 
		type: String, 
		default: null, 
	}, 
},

Create a setup section after the props and include the following code:

js
setup(props) {
	const calculatedValue = ref(0);

	if(props.sum){
		props.value.forEach(item => {
			const columns = props.column.split('.');

			columns.forEach(col => {
				item = item[col];
			});

			calculatedValue.value = calculatedValue.value + parseFloat(item);
		});
	} else {
		calculatedValue.value = props.value.length;
	}

	return { calculatedValue };
},
setup(props) {
	const calculatedValue = ref(0);

	if(props.sum){
		props.value.forEach(item => {
			const columns = props.column.split('.');

			columns.forEach(col => {
				item = item[col];
			});

			calculatedValue.value = calculatedValue.value + parseFloat(item);
		});
	} else {
		calculatedValue.value = props.value.length;
	}

	return { calculatedValue };
},

This code calculates the sum or count of the chosen column. The props.value will contain an array of objects with the fields defined in the scope. Make sure to return the constant at the bottom.

Update the template to use the calculateValue constant, prefix and suffix instead of the direct value.

vue
<template>
	<div>Value: {{ value }}</div> 
	<div v-if="calculatedValue">{{ prefix }}{{ calculateValue }}{{ suffix }}</div> 
	<value-null v-else /> 
</template>
<template>
	<div>Value: {{ value }}</div> 
	<div v-if="calculatedValue">{{ prefix }}{{ calculateValue }}{{ suffix }}</div> 
	<value-null v-else /> 
</template>

Build the display with the latest changes.

npm run build
npm run build

Add Display to Directus ​

When Directus starts, it will look in the extensions directory for any subdirectory starting with directus-extension-, and attempt to load them.

To install an extension, copy the entire directory with all source code, the package.json file, and the dist directory into the Directus extensions directory. Make sure the directory with your extension has a name that starts with directus-extension. In this case, you may choose to use directus-extension-display-sum-count.

Restart Directus to load the extension.

Required files

Only the package.json and dist directory are required inside of your extension directory. However, adding the source code has no negative effect.

Use the Display ​

Now the display will appear in the list of available displays for relational fields. Follow these steps to use the new display:

  1. Create a new relational field and select your new display from the list.
  2. After saving the new field, edit the field to configure the display and populate the fields as needed.
  3. Save changes and add some data to the table. You will see the relational fields at work in the layout.

In a table, a new field called 'Test Junction' is shown. The values are '5 items' and '2 items'.

Summary ​

With this display, you have learned how to interact with relational fields and values for a display and use options to customize the output. Be mindful of how much processing is happening inside a display because it will run for every single row in the table and will impact the performance of Directus.

Complete Code ​

index.js

js
import DisplayComponent from './display.vue';
import { useStores } from '@directus/extensions-sdk';

export default {
	id: 'directus-display-count-sum',
	name: 'Count or Sum Column',
	icon: '123',
	description: 'Count the related records or display the sum of the select column',
	component: DisplayComponent,
	options: ({ editing, relations }) => {
		const relatedCollection =
			relations.o2m?.meta.junction_field != null ? relations.m2o?.related_collection : relations.o2m?.collection;

		const junction_table = relations.o2m?.meta.junction_field != null ? relations.o2m?.collection : null;
		const { useFieldsStore } = useStores();
		const fieldsStore = useFieldsStore();

		let displayTemplateMeta;

		if (editing === '+') {
			 displayTemplateMeta = {
				interface: 'presentation-notice',
				options: {
					text: 'Please complete the field before attempting to configure the display.',
				},
				width: 'full',
			};
		} else {
			const fields = fieldsStore.getFieldsForCollection(relatedCollection);
			const field_choices = [];

			fields.forEach((field) => {
				field_choices.push({
					text: field.meta.field,
					value: junction_table ? `${relations.o2m.meta.junction_field}.${field.meta.field}` : field.meta.field,
				});
			});

			 displayTemplateMeta = {
				interface: 'select-dropdown',
				options: {
					choices: field_choices,
				},
				width: 'full',
			};
		}

		return [
			{
				field: 'column',
				name: 'Choose a column',
				meta: displayTemplateMeta,
			},
			{
				field: 'sum',
				type: 'boolean',
				name: 'Calulate Sum',
				meta: {
					interface: 'boolean',
					options: {
						label: 'Yes',
					},
					width: 'half',
				},
			},
			{
				field: 'prefix',
				type: 'string',
				name: 'Prefix',
				meta: {
					interface: 'input',
					options: {
						font: 'monospace',
					},
					width: 'half',
				},
			},
			{
				field: 'suffix',
				type: 'string',
				name: 'Suffix',
				meta: {
					interface: 'input',
					options: {
						font: 'monospace',
					},
					width: 'half',
				},
			},
		];
	},
	types: ['alias', 'string', 'uuid', 'integer', 'bigInteger', 'json'],
	localTypes: ['m2m', 'm2o', 'o2m', 'translations', 'm2a', 'file', 'files'],
	fields: (options) => {
		return [options.column];
	},
};
import DisplayComponent from './display.vue';
import { useStores } from '@directus/extensions-sdk';

export default {
	id: 'directus-display-count-sum',
	name: 'Count or Sum Column',
	icon: '123',
	description: 'Count the related records or display the sum of the select column',
	component: DisplayComponent,
	options: ({ editing, relations }) => {
		const relatedCollection =
			relations.o2m?.meta.junction_field != null ? relations.m2o?.related_collection : relations.o2m?.collection;

		const junction_table = relations.o2m?.meta.junction_field != null ? relations.o2m?.collection : null;
		const { useFieldsStore } = useStores();
		const fieldsStore = useFieldsStore();

		let displayTemplateMeta;

		if (editing === '+') {
			 displayTemplateMeta = {
				interface: 'presentation-notice',
				options: {
					text: 'Please complete the field before attempting to configure the display.',
				},
				width: 'full',
			};
		} else {
			const fields = fieldsStore.getFieldsForCollection(relatedCollection);
			const field_choices = [];

			fields.forEach((field) => {
				field_choices.push({
					text: field.meta.field,
					value: junction_table ? `${relations.o2m.meta.junction_field}.${field.meta.field}` : field.meta.field,
				});
			});

			 displayTemplateMeta = {
				interface: 'select-dropdown',
				options: {
					choices: field_choices,
				},
				width: 'full',
			};
		}

		return [
			{
				field: 'column',
				name: 'Choose a column',
				meta: displayTemplateMeta,
			},
			{
				field: 'sum',
				type: 'boolean',
				name: 'Calulate Sum',
				meta: {
					interface: 'boolean',
					options: {
						label: 'Yes',
					},
					width: 'half',
				},
			},
			{
				field: 'prefix',
				type: 'string',
				name: 'Prefix',
				meta: {
					interface: 'input',
					options: {
						font: 'monospace',
					},
					width: 'half',
				},
			},
			{
				field: 'suffix',
				type: 'string',
				name: 'Suffix',
				meta: {
					interface: 'input',
					options: {
						font: 'monospace',
					},
					width: 'half',
				},
			},
		];
	},
	types: ['alias', 'string', 'uuid', 'integer', 'bigInteger', 'json'],
	localTypes: ['m2m', 'm2o', 'o2m', 'translations', 'm2a', 'file', 'files'],
	fields: (options) => {
		return [options.column];
	},
};

display.vue

vue
<template>
	<div v-if="calculatedValue">{{ prefix }}{{ calculatedValue }}{{ suffix }}</div>
	<value-null v-else />
</template>

<script>
import { ref } from 'vue';
export default {
	props: {
		value: {
			type: Object,
			default: null,
		},
		column: {
			type: String,
			default: null,
		},
		sum: {
			type: Boolean,
			default: false,
		},
		prefix: {
			type: String,
			default: null,
		},
		suffix: {
			type: String,
			default: null,
		},
	},
	setup(props) {
		const calculatedValue = ref(0);

		if(props.sum){
			props.value.forEach(item => {
				const columns = props.column.split('.');

				columns.forEach(col => {
					item = item[col];
				});

				calculatedValue.value = calculatedValue.value + parseFloat(item);
			});
		} else {
			calculatedValue.value = props.value.length;
		}

		return { calculatedValue };
	},
};
</script>
<template>
	<div v-if="calculatedValue">{{ prefix }}{{ calculatedValue }}{{ suffix }}</div>
	<value-null v-else />
</template>

<script>
import { ref } from 'vue';
export default {
	props: {
		value: {
			type: Object,
			default: null,
		},
		column: {
			type: String,
			default: null,
		},
		sum: {
			type: Boolean,
			default: false,
		},
		prefix: {
			type: String,
			default: null,
		},
		suffix: {
			type: String,
			default: null,
		},
	},
	setup(props) {
		const calculatedValue = ref(0);

		if(props.sum){
			props.value.forEach(item => {
				const columns = props.column.split('.');

				columns.forEach(col => {
					item = item[col];
				});

				calculatedValue.value = calculatedValue.value + parseFloat(item);
			});
		} else {
			calculatedValue.value = props.value.length;
		}

		return { calculatedValue };
	},
};
</script>

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Tim Butterfield, Kevin Lewis
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