Extract data from structured string data


Strings fields may also contain structured data like JSON or Key-Value pairs. KQL provides easy access to these values for further analysis.

Dynamic Fields

Within a Log Analytics table, there are field types defined as Dynamic. Dynamic fields contain a key-value pair such as:

{"eventCategory":"Autoscale","eventName":"GetOperationStatusResult","operationId":"xxxxxxxx-6a53-4aed-bab4-575642a10226","eventProperties":"{\"OldInstancesCount\":6,\"NewInstancesCount\":5}","eventDataId":" xxxxxxxx -efe3-43c2-8c86-cd84f70039d3","eventSubmissionTimestamp":"2020-11-30T04:06:17.0503722Z","resource":"ch-appfevmss-pri","resourceGroup":"CH-RETAILRG-PRI","resourceProviderValue":"MICROSOFT.COMPUTE","subscriptionId":" xxxxxxxx -7fde-4caf-8629-41dc15e3b352","activityStatusValue":"Succeeded"}

To access the strings within a Dynamic field, use the dot notation. The DeviceDetail field from the SigninLogs table is of type dynamic. In this example, you could access the Operating System with the DeviceDetail.operatingSystem field name.

| extend OS = DeviceDetail.operatingSystem

The query example below shows the use of Dynamic fields with the SigninLogs table.

// Example query for SigninLogs showing how to break out packed fields.

| extend OS = DeviceDetail.operatingSystem, Browser = DeviceDetail.browser 
| extend StatusCode = tostring(Status.errorCode), StatusDetails = tostring(Status.additionalDetails) 
| extend Date = startofday(TimeGenerated) 
| summarize count() by Date, Identity, UserDisplayName, UserPrincipalName, IPAddress, ResultType, ResultDescription, StatusCode, StatusDetails 
| sort by Date


KQL provides functions to manipulate JSON stored in string fields. Many logs submit data in JSON format, which requires you to know how to transform JSON data to queryable fields.

The example below is a list of JSON related functions and operators.

Function Description
parse-json() or todynamic() Interprets a string as a JSON value and returns the value as dynamic. Use either of these functions to refer to a field: JsonField.Key or JsonField["Key"]
mv-expand is applied on a dynamic-typed array or property bag column so that each value in the collection gets a separate row. All the other columns in an expanded row are duplicated. mv_expand is the easiest way to process JSON arrays.
mv-apply Applies a subquery to each record and returns the union of the results of all subqueries. Apply a query to each value in an array.

Run each query separately to see the results.

| extend AuthDetails =  parse_json(AuthenticationDetails) 
| extend AuthMethod =  AuthDetails[0].authenticationMethod 
| extend AuthResult = AuthDetails[0].["authenticationStepResultDetail"] 
| project AuthMethod, AuthResult, AuthDetails 

| mv-expand AuthDetails = parse_json(AuthenticationDetails) 
| project AuthDetails

| mv-apply AuthDetails = parse_json(AuthenticationDetails) on
(where AuthDetails.authenticationMethod == "Password")