Dynamic templates in Elasticsearch - Step-by-Step Execution

Concept Flow - Dynamic templates

Start Index Mapping

↓

Receive Document Field

↓

Check Dynamic Templates

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Apply Template

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Map Field

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Continue for Next Field

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End

When a document is indexed, each field is checked against dynamic templates. If a template matches, it applies custom mapping; otherwise, default mapping is used.

Execution Sample

Elasticsearch

{
  "dynamic_templates": [
    {
      "strings_as_keywords": {
        "match_mapping_type": "string",
        "mapping": { "type": "keyword" }
      }
    }
  ]
}

This dynamic template maps all string fields as keyword type instead of the default text.

Execution Table

Step	Field Name	Field Type	Template Match?	Mapping Applied	Notes
1	title	string	Yes	keyword	Matches 'strings_as_keywords' template
2	views	long	No	long	No template matches, default mapping used
3	description	string	Yes	keyword	Matches template again
4	date	date	No	date	Default mapping for date type
5	tags	array of strings	Yes	keyword	Template applies to each string in array
6	END	-	-	-	All fields processed, mapping complete

💡 All document fields checked; dynamic templates applied where matched, default mapping otherwise.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	Final
field_name	-	title	views	description	date	tags	-
field_type	-	string	long	string	date	array of strings	-
template_match	-	Yes	No	Yes	No	Yes	-
mapping_applied	-	keyword	long	keyword	date	keyword	-

Key Moments - 3 Insights

Why does the 'views' field not match the dynamic template?

Because the template only matches fields of type 'string', and 'views' is a 'long' (number) type, so default mapping is used (see execution_table row 2).

How does the template apply to the 'tags' field which is an array?

Dynamic templates apply to each element in the array individually. Since 'tags' is an array of strings, each string matches the template and is mapped as 'keyword' (see execution_table row 5).

What happens if no dynamic template matches a field?

The field uses Elasticsearch's default mapping for its type, as shown for 'date' and 'views' fields (see execution_table rows 2 and 4).

Visual Quiz - 3 Questions

Look at the execution table, what mapping is applied to the 'description' field at step 3?

A text

B long

C keyword

D date

💡 Hint

Check the 'Mapping Applied' column at step 3 in the execution_table.

At which step does the condition 'Template Match?' become 'No' for the first time?

A Step 2

B Step 4

C Step 1

D Step 5

💡 Hint

Look at the 'Template Match?' column in the execution_table and find the first 'No'.

If the dynamic template was changed to match 'long' types instead of 'string', what would happen to the 'views' field mapping?

A It would be mapped as 'long' (default)

B It would be mapped as per the new template

C It would be mapped as 'keyword'

D It would cause an error

💡 Hint

Refer to variable_tracker and execution_table to see how template matching affects mapping.

Concept Snapshot

Dynamic templates let you customize how fields are mapped when indexing documents.
They check each field's type and name against rules.
If a template matches, its mapping is applied.
Otherwise, default mapping is used.
Useful to control indexing without defining full mappings upfront.

Full Transcript

Dynamic templates in Elasticsearch allow automatic mapping customization for fields during indexing. When a document is indexed, each field is checked against the dynamic templates defined in the index mapping. If a field matches a template's criteria, the mapping specified in that template is applied to the field. If no template matches, Elasticsearch applies its default mapping based on the field's data type. For example, a template can specify that all string fields should be mapped as keyword type instead of the default text type. This process repeats for every field in the document until all are mapped. This approach helps manage dynamic data with flexible mapping rules.