Object Storage Service (OSS) provides the data indexing feature to allow you to query objects that match specific metadata conditions, such as the name, ETag, storage class, size, and last modified time of objects. The data indexing feature sorts and aggregates the query results based on your business requirements. This improves the efficiency of querying specific objects from a large number of objects.
Usage notes
OSS SDK for Go 2.2.5 and later support the data indexing feature.
In this topic, the public endpoint of the China (Hangzhou) region is used. If you want to access OSS by using other Alibaba Cloud services in the same region as OSS, use an internal endpoint. For more information about the regions and endpoints supported by OSS, see Regions and endpoints.
In this topic, access credentials are obtained from environment variables. For more information about how to configure access credentials, see Configure access credentials.
In this topic, an OSSClient instance is created by using an OSS endpoint. If you want to create an OSSClient instance by using custom domain names or Security Token Service (STS), see Initialization.
Enable the metadata management feature for a bucket
The following code provides an example on how to enable the metadata management feature for a specific bucket. After you enable the metadata management feature for a bucket, OSS creates a metadata index library for the bucket and creates metadata indexes for all objects in the bucket. After the metadata index library is created, OSS continues to perform quasi-real-time scans on incremental objects in the bucket and creates metadata indexes for the incremental objects.
package main
import (
"fmt"
"github.com/aliyun/aliyun-oss-go-sdk/oss"
"os"
)
func main() {
// Obtain access credentials from environment variables. Before you run the sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are configured.
provider, err := oss.NewEnvironmentVariableCredentialsProvider()
if err != nil {
fmt.Println("Error:", err)
os.Exit(-1)
}
// Create an OSSClient instance.
// Specify the endpoint of the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the endpoint to https://oss-cn-hangzhou.aliyuncs.com. Specify your actual endpoint.
client, err := oss.New("yourEndpoint", "", "", oss.SetCredentialsProvider(&provider))
if err != nil {
fmt.Println("Error:", err)
os.Exit(-1)
}
// Enable the metadata management feature.
err = client.OpenMetaQuery("examplebucket")
if err != nil {
fmt.Println("Error:", err)
os.Exit(-1)
}
fmt.Println("Open data query success")
}Query the metadata index library of a bucket
The following code provides an example on how to query the metadata index library of a bucket:
package main
import (
"fmt"
"github.com/aliyun/aliyun-oss-go-sdk/oss"
"os"
)
func main() {
// Obtain access credentials from environment variables. Before you run the sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are configured.
provider, err := oss.NewEnvironmentVariableCredentialsProvider()
if err != nil {
fmt.Println("Error:", err)
os.Exit(-1)
}
// Create an OSSClient instance.
// Specify the endpoint of the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the endpoint to https://oss-cn-hangzhou.aliyuncs.com. Specify your actual endpoint.
client, err := oss.New("yourEndpoint", "", "", oss.SetCredentialsProvider(&provider))
if err != nil {
fmt.Println("Error:", err)
os.Exit(-1)
}
// Query information about the metadata index library.
result, err := client.GetMetaQueryStatus("examplebucket")
if err != nil {
fmt.Println("Error:", err)
os.Exit(-1)
}
fmt.Printf("State:%s\n", result.State)
fmt.Printf("Phase:%s\n", result.Phase)
fmt.Printf("CreateTime:%s\n", result.CreateTime)
fmt.Printf("UpdateTime:%s\n", result.UpdateTime)
}
Query objects that meet specified conditions
The following code provides an example on how to query objects that meet specified conditions and list the object information based on the specified fields and sorting methods:
package main
import (
"fmt"
"github.com/aliyun/aliyun-oss-go-sdk/oss"
"os"
)
func main() {
// Obtain access credentials from environment variables. Before you run the sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are configured.
provider, err := oss.NewEnvironmentVariableCredentialsProvider()
if err != nil {
fmt.Println("Error:", err)
os.Exit(-1)
}
// Create an OSSClient instance.
// Specify the endpoint of the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the endpoint to https://oss-cn-hangzhou.aliyuncs.com. Specify your actual endpoint.
client, err := oss.New("yourEndpoint", "", "", oss.SetCredentialsProvider(&provider))
if err != nil {
fmt.Println("Error:", err)
os.Exit(-1)
}
// Query objects that are larger than 30 bytes in size, return up to 10 objects at the same time, and then sort the objects in ascending order.
query := oss.MetaQuery{
NextToken: "",
MaxResults: 10,
Query: `{"Field": "Size","Value": "30","Operation": "gt"}`,
Sort: "Size",
Order: "asc",
}
// Query objects that match the specified conditions and list object information based on the specified fields and sorting methods.
result,err := client.DoMetaQuery("examplebucket",query)
if err != nil {
fmt.Println("Error:", err)
os.Exit(-1)
}
fmt.Printf("NextToken:%s\n", result.NextToken)
for _, file := range result.Files {
fmt.Printf("File name: %s\n", file.Filename)
fmt.Printf("size: %d\n", file.Size)
fmt.Printf("File Modified Time:%s\n", file.FileModifiedTime)
fmt.Printf("Oss Object Type:%s\n", file.OssObjectType)
fmt.Printf("Oss Storage Class:%s\n", file.OssStorageClass)
fmt.Printf("Object ACL:%s\n", file.ObjectACL)
fmt.Printf("ETag:%s\n", file.ETag)
fmt.Printf("Oss CRC64:%s\n", file.OssCRC64)
fmt.Printf("Oss Tagging Count:%d\n", file.OssTaggingCount)
for _, tagging := range file.OssTagging {
fmt.Printf("Oss Tagging Key:%s\n", tagging.Key)
fmt.Printf("Oss Tagging Value:%s\n", tagging.Value)
}
for _, userMeta := range file.OssUserMeta {
fmt.Printf("Oss User Meta Key:%s\n", userMeta.Key)
fmt.Printf("Oss User Meta Key Value:%s\n", userMeta.Value)
}
}
}Disable the metadata management feature for a bucket
The following code provides an example on how to disable the metadata management feature for a specific bucket:
package main
import (
"fmt"
"github.com/aliyun/aliyun-oss-go-sdk/oss"
"os"
)
func main() {
/// Obtain access credentials from environment variables. Before you run the sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are configured.
provider, err := oss.NewEnvironmentVariableCredentialsProvider()
if err != nil {
fmt.Println("Error:", err)
os.Exit(-1)
}
// Create an OSSClient instance.
// Specify the endpoint of the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the endpoint to https://oss-cn-hangzhou.aliyuncs.com. Specify your actual endpoint.
client, err := oss.New("yourEndpoint", "", "", oss.SetCredentialsProvider(&provider))
if err != nil {
fmt.Println("Error:", err)
os.Exit(-1)
}
// Disable the metadata management feature.
err = client.CloseMetaQuery("examplebucket")
if err != nil {
fmt.Println("Error:", err)
os.Exit(-1)
}
fmt.Println("Closed data query success")
}References
For more information about the API operation for enabling the metadata management feature, see OpenMetaQuery.
For more information about the API operation for querying a metadata index library, see GetMetaQueryStatus.
For more information about the API operation for querying objects that meet specified conditions and listing objects by specified field and sorting method, see DoMetaQuery.
For more information about the API operation for disabling the metadata management feature, see CloseMetaQuery.