Date field types in Elasticsearch - Mini Project: Build & Apply

Date Field Types in Elasticsearch

📖 Scenario: You are working with Elasticsearch to store and search event data. Each event has a date field that needs to be stored correctly so you can query by date later.

🎯 Goal: Create an Elasticsearch index mapping with a date field type. Then add a document with a date value and finally query the document by date.

📋 What You'll Learn

Create an index mapping with a date field called event_date

Use the strict_date_optional_time||epoch_millis format for the date field

Index a document with event_date set to 2023-12-25T10:00:00Z

Query the document by matching the event_date field

💡 Why This Matters

🌍 Real World

Storing and searching events, logs, or any data with dates is common in many applications like calendars, monitoring systems, and analytics.

💼 Career

Understanding date field types in Elasticsearch is essential for backend developers, data engineers, and anyone working with search and analytics platforms.

1

Create index mapping with date field

Create an index called events with a mapping that defines a date field named event_date using the format strict_date_optional_time||epoch_millis. Use the PUT method and JSON body as shown.

Elasticsearch

# Use PUT /events with mapping for event_date as date type
# Your code here

Hint

Use PUT /events to create the index. Inside mappings, define properties with event_date as type: date and set the format.

2

Index a document with event_date

Index a document into the events index with event_date set to "2023-12-25T10:00:00Z". Use the POST method on /events/_doc with the JSON body.

Elasticsearch

PUT /events
{
  "mappings": {
    "properties": {
      "event_date": {
        "type": "date",
        "format": "strict_date_optional_time||epoch_millis"
      }
    }
  }
}

# Index a document with event_date
# Your code here

Hint

Use POST /events/_doc to add a document. The JSON body must have event_date with the exact date string.

3

Query document by event_date

Write a search query on the events index to find documents where event_date matches "2023-12-25T10:00:00Z". Use the GET method on /events/_search with a match query on event_date.

Elasticsearch

PUT /events
{
  "mappings": {
    "properties": {
      "event_date": {
        "type": "date",
        "format": "strict_date_optional_time||epoch_millis"
      }
    }
  }
}

POST /events/_doc
{
  "event_date": "2023-12-25T10:00:00Z"
}

# Search for document by event_date
# Your code here

Hint

Use GET /events/_search with a JSON body containing a match query on event_date with the exact date string.

4

Display search results

Print the JSON response from the search query to show the matched document with event_date "2023-12-25T10:00:00Z".

Elasticsearch

PUT /events
{
  "mappings": {
    "properties": {
      "event_date": {
        "type": "date",
        "format": "strict_date_optional_time||epoch_millis"
      }
    }
  }
}

POST /events/_doc
{
  "event_date": "2023-12-25T10:00:00Z"
}

GET /events/_search
{
  "query": {
    "match": {
      "event_date": "2023-12-25T10:00:00Z"
    }
  }
}

# Show the search response here
# Your code here

Hint

The search response JSON should include the document with event_date set to "2023-12-25T10:00:00Z".

Practice

1. What is the primary purpose of a date field type in Elasticsearch?

easy

A. To store and query time and date information

B. To store large text documents

C. To perform mathematical calculations

D. To store binary data

Solution

1. Step 1: Understand the role of field types in Elasticsearch

   Field types define how data is stored and interpreted in Elasticsearch.

2. Step 2: Identify the function of the date field type

   The date field type specifically stores time and date information for searching and sorting.

3. Final Answer:

   To store and query time and date information -> Option A

4. Quick Check:

   Date field = store time/date [OK]

Hint: Date fields store time info, not text or numbers [OK]

Common Mistakes:

• Confusing date fields with text fields
• Thinking date fields store binary data
• Assuming date fields perform calculations

2. Which of the following is the correct way to define a date field with a custom format in an Elasticsearch mapping?

easy

A. {
"mappings": {
"properties": {
"created_at": {"type": "integer", "format": "yyyy-MM-dd"}
}
}
}

B. {
"mappings": {
"properties": {
"created_at": {"type": "date", "format": "yyyy-MM-dd HH:mm:ss"}
}
}
}

C. {
"mappings": {
"properties": {
"created_at": {"type": "date"}
}
}
}

D. {
"mappings": {
"properties": {
"created_at": {"type": "text", "format": "yyyy-MM-dd"}
}
}
}

Solution

1. Step 1: Check the field type for date

   The field must have type set to date to store dates.

2. Step 2: Verify the format property

   Custom date formats are specified with the format key inside the date field definition.

3. Final Answer:

   Mapping with type 'date' and format 'yyyy-MM-dd HH:mm:ss' -> Option B

4. Quick Check:

   Date type + format key = correct mapping [OK]

Hint: Date fields need type 'date' and format string [OK]

Common Mistakes:

• Using type 'text' or 'integer' for date fields
• Omitting the format when using custom date strings
• Placing format outside the date field definition

3. Given this Elasticsearch mapping and document, what will be the stored value for the event_date field?

{
  "mappings": {
    "properties": {
      "event_date": { "type": "date", "format": "yyyy/MM/dd" }
    }
  }
}

Document:
{
  "event_date": "2024/06/15"
}

medium

A. Error: Invalid date format

B. "2024/06/15"

C. "2024-06-15T00:00:00.000Z"

D. "15-06-2024"

Solution

1. Step 1: Understand the mapping format

   The mapping expects dates in the format "yyyy/MM/dd" which matches the document date "2024/06/15".

2. Step 2: Know how Elasticsearch stores dates internally

   Elasticsearch converts dates to ISO 8601 format with time and timezone, so it stores "2024-06-15T00:00:00.000Z".

3. Final Answer:

   "2024-06-15T00:00:00.000Z" -> Option C

4. Quick Check:

   Input format matches mapping, stored as ISO date [OK]

Hint: Input matches format, stored as ISO 8601 date [OK]

Common Mistakes:

• Expecting stored value to keep original format
• Thinking Elasticsearch stores raw string
• Confusing format mismatch errors

4. You defined a date field with format yyyy-MM-dd but indexing documents with dates like 2024/06/15 causes errors. What is the best fix?

medium

A. Change the mapping format to include yyyy/MM/dd

B. Convert all dates to yyyy-MM-dd before indexing

C. Change the field type to text

D. Remove the format from the mapping

Solution

1. Step 1: Identify the cause of the error

   The document dates use slashes / but the mapping expects dashes -, causing format mismatch errors.

2. Step 2: Fix the mapping to accept the document date format

   Update the mapping format to include yyyy/MM/dd so Elasticsearch can parse the input dates correctly.

3. Final Answer:

   Change the mapping format to include yyyy/MM/dd -> Option A

4. Quick Check:

   Mapping format must match input date format [OK]

Hint: Mapping format must match input date format exactly [OK]

Common Mistakes:

• Changing field type to text loses date features
• Removing format causes parsing errors if format differs
• Not updating mapping when input format changes

5. You want to index documents with multiple date fields: created_at in ISO format and due_date in dd-MM-yyyy format. How should you define the mapping to handle both correctly?

hard

A. {
"mappings": {
"properties": {
"created_at": { "type": "date", "format": "dd-MM-yyyy" },
"due_date": { "type": "date" }
}
}
}

B. {
"mappings": {
"properties": {
"created_at": { "type": "date", "format": "dd-MM-yyyy" },
"due_date": { "type": "date", "format": "dd-MM-yyyy" }
}
}
}

C. {
"mappings": {
"properties": {
"created_at": { "type": "text" },
"due_date": { "type": "text" }
}
}
}

D. {
"mappings": {
"properties": {
"created_at": { "type": "date" },
"due_date": { "type": "date", "format": "dd-MM-yyyy" }
}
}
}

Solution

1. Step 1: Understand the formats of each date field

   created_at uses ISO format (default), due_date uses custom dd-MM-yyyy format.

2. Step 2: Define mapping with correct formats per field

   Set created_at as date with default format, and due_date as date with format: dd-MM-yyyy.

3. Final Answer:

   Mapping with default date for created_at and custom format for due_date -> Option D

4. Quick Check:

   Each date field needs correct format in mapping [OK]

Hint: Set format per date field to match its input format [OK]

Common Mistakes:

• Using text type instead of date loses date features
• Applying wrong format to a field causes parsing errors
• Using same format for different date formats