Hydrate Functions

A hydrate function connects to an external system or service and gathers data to fill a database table.

List and Get and are hydrate functions, defined in the Table Definition, that have these special characteristics:

  • Every table must define a List and/or Get function.

  • The List or Get will always be called before any other hydrate function in the table, as the other functions typically depend on the result of the Get or List call.

  • Whether List or Get is called depends upon whether the qualifiers (in where clauses and join...on) match the KeyColumns defined in the Get Config. This enables Steampipe to fetch only the "row" data that it needs.

  • Typically, hydrate functions return a single data item (data for a single row). List functions are an exception — they stream data for multiple rows using the QueryData object, and return nil.

  • The Get function will usually get the key column data from the QueryData.KeyColumnQuals so that it can get the appropriate item as based on the qualifiers (where clause, join...on). If the Get hydrate function is used as both a Get function AND a normal hydrate function, you should get the key column data from the HydrateData.Item if it is not nil, and use the QueryData.KeyColumnQuals otherwise.

About List Functions

A List function retrieves all the items of a particular resource type from an API. For example, the zendesk_group table supports the query:

select
*
from
zendesk_group

The function tableZenDeskGroup defines the table.

package zendesk
import (
"context"
"github.com/turbot/steampipe-plugin-sdk/v5/grpc/proto"
"github.com/turbot/steampipe-plugin-sdk/v5/plugin"
)
func tableZendeskGroup() *plugin.Table {
return &plugin.Table{
Name: "zendesk_group",
Description: "When support requests arrive in Zendesk Support, they can be assigned to a Group. Groups serve as the core element of ticket workflow; support agents are organized into Groups and tickets can be assigned to a Group only, or to an assigned agent within a Group. A ticket can never be assigned to an agent without also being assigned to a Group.",
List: &plugin.ListConfig{
Hydrate: listGroup,
},
Get: &plugin.GetConfig{
KeyColumns: plugin.SingleColumn("id"),
Hydrate: getGroup,
},
Columns: []*plugin.Column{
{Name: "id", Type: proto.ColumnType_INT, Description: "Unique identifier for the group"},
{Name: "url", Type: proto.ColumnType_STRING, Description: "API url of the group"},
{Name: "name", Type: proto.ColumnType_STRING, Description: "Name of the group"},
{Name: "deleted", Type: proto.ColumnType_BOOL, Description: "True if the group has been deleted"},
{Name: "created_at", Type: proto.ColumnType_TIMESTAMP, Description: "The time the group was created"},
{Name: "updated_at", Type: proto.ColumnType_TIMESTAMP, Description: "The time of the last update of the group"},
},
}
}

The table's List property refers, by way of the Hydrate property, to a Steampipe function that lists Zendesk groups, listGroup. That function calls the GitHub Go SDK's GetGroups and returns an array of Group.

type Group struct {
ID int64 `json:"id,omitempty"`
URL string `json:"url,omitempty"`
Name string `json:"name"`
Default bool `json:"default,omitempty"`
Deleted bool `json:"deleted,omitempty"`
Description string `json:"description,omitempty"`
CreatedAt time.Time `json:"created_at,omitempty"`
UpdatedAt time.Time `json:"updated_at,omitempty"`
}

A Steampipe List function is one of two special forms of hydrate functionGet is the other — that take precedence over other hydrate functions.

About Get Functions

A Get function fetches a single item by its key. While it's possible to define a table that only uses Get, the common pattern combines List to retrieve basic data and Get to enrich it. Here's the Get function for a Zendesk group.

func getGroup(ctx context.Context, d *plugin.QueryData, h *plugin.HydrateData) (interface{}, error) {
conn, err := connect(ctx, d)
if err != nil {
return nil, err
}
quals := d.EqualsQuals
id := quals["id"].GetInt64Value()
result, err := conn.GetGroup(ctx, id)
if err != nil {
return nil, err
}
return result, nil
}

Observing List versus Get

When List and Get are both defined, you can use diagnostic mode to see which function Steampipe calls for a given query.

STEAMPIPE_DIAGNOSTIC_LEVEL=all steampipe service start

This query uses List.

> select jsonb_pretty(_ctx) as _ctx from zendesk_group limit 1
+--------------------------------------------------+
| _ctx |
+--------------------------------------------------+
| { |
| "steampipe": { |
| "sdk_version": "5.8.0" |
| }, |
| "diagnostics": { |
| "calls": [ |
| { |
| "type": "list", |
| "scope_values": { |
| "table": "zendesk_group", |
| "connection": "zendesk", |
| "function_name": "listGroup" |
| }, |
| "function_name": "listGroup", |
| "rate_limiters": [ |
| ], |
| "rate_limiter_delay_ms": 0 |
| } |
| ] |
| }, |
| "connection_name": "zendesk" |
| } |
+--------------------------------------------------+

This query uses Get.

> select jsonb_pretty(_ctx) as _ctx from zendesk_group where id = '24885656597005'
+--------------------------------------------------+
| _ctx |
+--------------------------------------------------+
| { |
| "steampipe": { |
| "sdk_version": "5.8.0" |
| }, |
| "diagnostics": { |
| "calls": [ |
| { |
| "type": "list", |
| "scope_values": { |
| "table": "zendesk_group", |
| "connection": "zendesk", |
| "function_name": "getGroup" |
| }, |
| "function_name": "getGroup", |
| "rate_limiters": [ |
| ], |
| "rate_limiter_delay_ms": 0 |
| } |
| ] |
| }, |
| "connection_name": "zendesk" |
| } |
+--------------------------------------------------+

This works because id is one of the KeyColumns in the Get property of the table definition.

Get: &plugin.GetConfig{
KeyColumns: plugin.SingleColumn("id"),
Hydrate: getGroup,
},

That enables the Steampipe plugin SDK to choose the more optimal getGroup function when the id is known.

List or Get in Combination with Hydrate

In addition to the special List and Get hydrate functions, there's a class of general hydrate functions that enrich what's returned by List or Get. The Zendesk plugin doesn't use any of these, but in table_aws_cloudtrail_trail.go, getCloudTrailStatus is an example of this kind of function.

Steampipe knows it's a HydrateFunc because the column definition declares it using the Hydrate property.

{
Name: "latest_cloudwatch_logs_delivery_error",
Description: "Displays any CloudWatch Logs error that CloudTrail encountered when attempting to deliver logs to CloudWatch Logs.",
Type: proto.ColumnType_STRING,
Hydrate: getCloudtrailTrailStatus,
Transform: transform.FromField("LatestCloudWatchLogsDeliveryError"),
},

HydrateConfig

Use HydrateConfig in a table definition to provide granular control over the behavior of a hydrate function.

Things you can control with a HydrateConfig:

  • Errors to ignore.

  • Errors to retry.

  • Max concurrent calls to allow.

  • Hydrate dependencies

  • Rate-limiter tags

For a Get or List, you can specify errors to ignore and/or retry using DefaultIgnoreConfig and DefaultRetryConfig as seen here in the Fastly plugin.

func Plugin(ctx context.Context) *plugin.Plugin {
p := &plugin.Plugin{
Name: "steampipe-plugin-fastly",
ConnectionConfigSchema: &plugin.ConnectionConfigSchema{
NewInstance: ConfigInstance,
},
DefaultTransform: transform.FromGo().NullIfZero(),
DefaultIgnoreConfig: &plugin.IgnoreConfig{
ShouldIgnoreErrorFunc: shouldIgnoreErrors([]string{"404"}),
},
DefaultRetryConfig: &plugin.RetryConfig{
ShouldRetryErrorFunc: shouldRetryError([]string{"429"}),
},
TableMap: map[string]*plugin.Table{
"fastly_acl": tableFastlyACL(ctx),
...
"fastly_token": tableFastlyToken(ctx),
},
}
return p
}

For other hydrate functions, you do this with HydrateConfig. Here's how the oci_identity_tenancy table configures error handling for the getRetentionPeriod function.

HydrateConfig: []plugin.HydrateConfig{
{
Func: getRetentionPeriod,
ShouldIgnoreError: isNotFoundError([]string{"404"}),
},
},

You can similarly use ShouldRetryError along with a corresponding function that returns true if, for example, an API call its a rate limit.

func shouldRetryError(err error) bool {
if cloudflareErr, ok := err.(*cloudflare.APIRequestError); ok {
return cloudflareErr.ClientRateLimited()
}
return false
}

You can likewise use MaxConcurrency to limit the number of calls to a hydrate function.

In practice, the granular controls afforded by ShouldIgnoreError, ShouldRetryError, and MaxConcurrency are not much used at the level of individual hydrate functions. Plugins are likelier to assert such control globally. But the flexibility is threre if you need it.

Two features of HydrateConfig that are used quite a bit are Depends and Tags.

Use Depends to make a function depend on one or more others. In aws_s3_bucket, the function getBucketLocation returns the client region that's needed by all the other functions, so they all depend on it.

HydrateConfig: []plugin.HydrateConfig{
{
Func: getBucketLocation,
Tags: map[string]string{"service": "s3", "action": "GetBucketLocation"},
},
{
Func: getBucketIsPublic,
Depends: []plugin.HydrateFunc{getBucketLocation},
Tags: map[string]string{"service": "s3", "action": "GetBucketPolicyStatus"},
},
{
Func: getBucketVersioning,
Depends: []plugin.HydrateFunc{getBucketLocation},
Tags: map[string]string{"service": "s3", "action": "GetBucketVersioning"},
},

Use Tags to expose a hydrate function to control by a limiter. In AWS plugin's, aws_config_rule table, the HydrateConfig specifies additional hydrate functions that fetch tags and compliance details for each config rule.

HydrateConfig:plugin.HydrateConfig{
{
Func: getConfigRuleTags,
Tags: map[string]string{"service": "config", "action": "ListTagsForResource"},
},
{
Func: getComplianceByConfigRules,
Tags: map[string]string{"service": "config", "action": "DescribeComplianceByConfigRule"},
},
},

In this example the Func property names getConfigRuleTags and getComplianceByConfigRules as additional hydrate functions that fetch tags and compliance details for each config rule, respectively. The Tags property enables a rate limiter to target these functions. (See also function-tags below.)

Memoize: Caching hydrate results

The Memoize function can be used to cache the results of a HydrateFunc.

In the multi_region.go file of steampipe-plugin-aws repository, the listRegionsForServiceCacheKey function is used to create a custom cache key for the listRegionsForService function. This cache key includes the service ID, which is unique for each AWS service.

Here's a simplified version of the code:

func listRegionsForServiceCacheKey(ctx context.Context, d *plugin.QueryData, h *plugin.HydrateData) (interface{}, error) {
serviceID := h.Item.(string)
key := fmt.Sprintf("listRegionsForService-%s", serviceID)
return key, nil
}
var listRegionsForService = plugin.HydrateFunc(listRegionsForServiceUncached).Memoize(memoize.WithCacheKeyFunction(listRegionsForServiceCacheKey))

In this example, Memoize caches the results of listRegionsForServiceUncached. The WithCacheKeyFunction option specifies a custom function (listRegionsForServiceCacheKey) to generate the cache key. This function takes the service ID from the hydrate data and includes it in the cache key, ensuring a unique cache key for each AWS service.

This is a common pattern when using Memoize: you define a HydrateFunc and then wrap it with Memoize to enable caching. You can also use the WithCacheKeyFunction option to specify a custom function that generates the cache key, which is especially useful when you need to include additional context in the cache key.

Additional functions can be chained after a From function to transform the data:

NameDescription
TransformApply an arbitrary transform to the data (specified by 'transformFunc').
TransformPApply an arbitrary transform to the data, passing a parameter.
NullIfEqualIf the input value equals the transform param, return nil.
NullIfZeroIf the input value equals the zero value of its type, return nil.