Get a collection by name

Use the Collection method on a db.Session to get a reference to a specific collection:

col := sess.Collection("books")

A collection reference satisfies db.Collection and gives you access to a set of methods for retrieving and manipulating data, such as Find (to search for specific records in the collection) and Insert (to add more records to a collection).

Note that if you create a reference to a collection that doesn’t exist, you’ll see a warning message:

2020/07/01 00:11:33 upper/db: log_level=WARNING file=/go/src/git...
 Session ID:     00001
 Query:          SELECT "pg_attribute"."attname" AS "pkey" ...
 Error:          pq: relation "fake_collection" does not exist
 Time taken:     0.00129s
 Context:        context.Background

If you’d prefer not to see warning messages, set a higher logging level:

db.LC().SetLevel(db.LogLevelError)

Use the Exists method to check whether a collection exists or not:

exists, err := collection.Exists()
if errors.Is(err, db.ErrCollectionDoesNotExist) {
 log.Printf("Collection does not exist: %v", err)
}

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              package main

import (
	"fmt"
	"log"

	"github.com/upper/db/v4/adapter/postgresql"
)

var settings = postgresql.ConnectionURL{
	Database: "booktown",
	Host:     "postgres",
	User:     "demo",
	Password: "b4dp4ss",
	Options: map[string]string{
		"sslmode": "disable", // Disable TLS
	},
}

func main() {
	sess, err := postgresql.Open(settings)
	if err != nil {
		log.Fatal("Open: ", err)
	}
	defer sess.Close()

	// The Collection method returns a reference to a specific collection in the
	// database. In this case, the collection is a table named "books".
	col := sess.Collection("books")

	// Get the name of the collection.
	fmt.Printf("The name of the collection is %q.\n", col.Name())

	// You can create references to collections that don't exist (yet). That
	// might be useful when working with document-based databases.
	nonExistentCollection := sess.Collection("fake")
	ok, err := nonExistentCollection.Exists()
	fmt.Printf("Q: Does collection %q exists?\n", nonExistentCollection.Name())
	fmt.Printf("R: %v (%v)", ok, err)
}

            