Object Storage Service:Query files using OSS SDK for Go 2.0

Prerequisites

Before you begin, make sure you have:

• An OSS bucket in the cn-hangzhou region (or another supported region)

• The oss:GetObject permission on the target object. For details, see Grant custom permissions to a RAM user

• Access credentials configured as environment variables. For details, see Configure access credentials

Limitations

• Only CSV and JSON files are supported as input.

• The sample code uses the cn-hangzhou region with a public endpoint. To access OSS from another Alibaba Cloud service in the same region, use the internal endpoint instead. For a full list of regions and endpoints, see Regions and endpoints.

How it works

Each SelectObject request requires two configuration objects:

• Input serialization (InputSerializationSelect): Specifies the format of the source file — CSV or JSON — and how to parse it. For CSV files, set FileHeaderInfo to Use to treat the first row as a column header. For JSON files, set JSONType to DOCUMENT for a single JSON object.

• Output serialization (OutputSerializationSelect): Controls the format of the query result. Set OutputHeader to true to include column headers in the output.

The SQL expression uses ossobject as the table alias. For example, select * from ossobject limit 10 returns the first 10 rows.

The result is returned as a stream. Use io.ReadAll to read it fully into memory.

Method definition

func (c *Client) SelectObject(ctx context.Context, request *SelectObjectRequest, optFns ...func(*Options)) (*SelectObjectResult, error)

Sample code

package main

import (
	"context"
	"flag"
	"io"
	"log"

	"github.com/aliyun/alibabacloud-oss-go-sdk-v2/oss"
	"github.com/aliyun/alibabacloud-oss-go-sdk-v2/oss/credentials"
)

// Define global variables.
var (
	region     string // The storage region.
	bucketName string // The bucket name.
	objectName string // The object name.
)

// The init function is used to initialize command line parameters.
func init() {
	flag.StringVar(&region, "region", "", "The region in which the bucket is located.")
	flag.StringVar(&bucketName, "bucket", "", "The name of the bucket.")
	flag.StringVar(&objectName, "object", "", "The name of the object.")
}

func main() {
	// Parse command line parameters.
	flag.Parse()

	// Check whether the bucket name is empty.
	if len(bucketName) == 0 {
		flag.PrintDefaults()
		log.Fatalf("invalid parameters, bucket name required")
	}

	// Check whether the region is empty.
	if len(region) == 0 {
		flag.PrintDefaults()
		log.Fatalf("invalid parameters, region required")
	}

	// Check whether the object name is empty.
	if len(objectName) == 0 {
		flag.PrintDefaults()
		log.Fatalf("invalid parameters, object name required")
	}

	// Load the default configurations and set the credential provider and region.
	cfg := oss.LoadDefaultConfig().
		WithCredentialsProvider(credentials.NewEnvironmentVariableCredentialsProvider()).
		WithRegion(region)

	// Create an OSS client.
	client := oss.NewClient(cfg)

	// Create a request to select an object.
	request := &oss.SelectObjectRequest{
		Bucket: oss.Ptr(bucketName), // The bucket name.
		Key:    oss.Ptr(objectName), // The object name.
		SelectRequest: &oss.SelectRequest{
			Expression: oss.Ptr("select * from ossobject limit 10"), // Define an SQL expression to query the first 10 rows of data in the object.
			InputSerializationSelect: oss.InputSerializationSelect{
				CsvBodyInput: &oss.CSVSelectInput{
					FileHeaderInfo: oss.Ptr("Use"),
				},
			},
			OutputSerializationSelect: oss.OutputSerializationSelect{
				OutputHeader: oss.Ptr(true),
			},
		},
	}

	// Execute the request to select the object.
	result, err := client.SelectObject(context.TODO(), request)
	if err != nil {
		log.Fatalf("failed to select object %v", err)
	}

	content, err := io.ReadAll(result.Body)
	if err != nil {
		log.Fatalf("failed to read object %v", err)
	}

	// Print the result of selecting the object.
	log.Printf("select object result:%#v\n", string(content))
}

package main

import (
	"context"
	"flag"
	"io"
	"log"

	"github.com/aliyun/alibabacloud-oss-go-sdk-v2/oss"
	"github.com/aliyun/alibabacloud-oss-go-sdk-v2/oss/credentials"
)

// Define global variables.
var (
	region     string // The storage region.
	bucketName string // The bucket name.
	objectName string // The object name.
)

// The init function is used to initialize command line parameters.
func init() {
	flag.StringVar(&region, "region", "", "The region in which the bucket is located.")
	flag.StringVar(&bucketName, "bucket", "", "The name of the bucket.")
	flag.StringVar(&objectName, "object", "", "The name of the object.")
}

func main() {
	// Parse command line parameters.
	flag.Parse()

	// Check whether the bucket name is empty.
	if len(bucketName) == 0 {
		flag.PrintDefaults()
		log.Fatalf("invalid parameters, bucket name required")
	}

	// Check whether the region is empty.
	if len(region) == 0 {
		flag.PrintDefaults()
		log.Fatalf("invalid parameters, region required")
	}

	// Check whether the object name is empty.
	if len(objectName) == 0 {
		flag.PrintDefaults()
		log.Fatalf("invalid parameters, object name required")
	}

	// Load the default configurations and set the credential provider and region.
	cfg := oss.LoadDefaultConfig().
		WithCredentialsProvider(credentials.NewEnvironmentVariableCredentialsProvider()).
		WithRegion(region)

	// Create an OSS client.
	client := oss.NewClient(cfg)

	// Create a request to select an object.
	request := &oss.SelectObjectRequest{
		Bucket: oss.Ptr(bucketName), // The bucket name.
		Key:    oss.Ptr(objectName), // The object name.
		SelectRequest: &oss.SelectRequest{
			Expression: oss.Ptr("select * from ossobject limit 10"), // Define an SQL expression to query the first 10 rows of data in the object.
			InputSerializationSelect: oss.InputSerializationSelect{
				JsonBodyInput: &oss.JSONSelectInput{
					JSONType: oss.Ptr("DOCUMENT"),
				},
			},
			OutputSerializationSelect: oss.OutputSerializationSelect{
				OutputHeader: oss.Ptr(true),
			},
		},
	}

	// Send the request to select the object.
	result, err := client.SelectObject(context.TODO(), request)
	if err != nil {
		log.Fatalf("failed to select object %v", err)
	}

	content, err := io.ReadAll(result.Body)
	if err != nil {
		log.Fatalf("failed to read object %v", err)
	}

	// Print the result of selecting the object.
	log.Printf("select object result:%#v\n", string(content))
}

Error handling

If SelectObject returns an error, inspect the error message for details. For the complete API reference, see SelectObject.

What's next

• For the complete sample code, see GitHub sample.

• For the full API reference, see SelectObject.

• For an overview of the SelectObject feature, see Query files.