Agnostic data API

The db package provides an agnostic Go API focused on working with collections of items. This API is modelled after basic set theory concepts that are applicable to relational and document-based database engines alike.

Using db you can create a database session and use all of the db.Session methods.

The Collection() method of db.Session takes a collection name and returns an reference that you can use to do simple operations on that collection:

// Reference to a table/collection named "people"
people := sess.Collection("people")
...

log.Printf("The name of the collection is: %s", people.Name())

Collections are sets of items of a particular kind. In order to make it easier to work with concepts from both SQL and NoSQL databases, upper/db refers to both NoSQL collections and SQL tables as "collections".

The example below demonstrates how to explore all collections in the database and create collection references:

package main import ( "fmt" "log" "github.com/upper/db/v4/adapter/postgresql" ) var settings = postgresql.ConnectionURL{ Database: "booktown", Host: "demo.upper.io", User: "demouser", Password: "demop4ss", } func main() { sess, err := postgresql.Open(settings) if err != nil { log.Fatal("Open: ", err) } defer sess.Close() // Retrieve the names of all the collections. collections, err := sess.Collections() if err != nil { log.Fatal("Collections: ", err) } // Iterate over the names of all the collections and get collection // references. for _, collection := range collections { fmt.Printf("Collection: %q\n", collection.Name()) } }

Working with collections (CRUD)

Find

A result-set is a subset of items from a collection. If you have a collection reference you can create a result set by using the Find() method:

// Collection reference
col := sess.Collection("people")

// Requesting all items in the "people" collection
res := col.Find()
...

// String-like syntax is accepted.
res = col.Find("id", 25)

// Equality is the default operator but a different one can be used.
res = col.Find("id >", 29)

// The `?` placeholder maps arguments by order.
res = col.Find("id > ? AND id < ?", 20, 39)

// You can add more conditions to `Find()` with `And()`
res = col.Find("id >", 20).And("id <", 39)

// Primary keys can also be passed as arguments.
res = col.Find(20)

A result-set reference provides simple operations like All(), One(), Delete() and Update() that allow you to work easily with all the items that belong to the result set.

Use All() on result-sets to retrieve and map all the results into a slice:

var users []User

err := res.All(&users)
...

Or One to retrieve and map only one element:

var user User

err := res.One(&user)
...

Using Find() with no arguments creates a result set containing all items in the collection.

res = col.Find()
...
err = res.All(&items)
...

This other result set has a constraint, only items with id = 11 will be part of the result set.

res = col.Find(db.Cond{"id": 11})
...
err = res.One(&item)
...

This Find() call does the same as above with a shorter syntax only supported by SQL adapters.

res = col.Find("id", 11)
...

If you're dealing with a relatively small number of items, you may want to dump them all at once, use the All() method on a result-set to do so, like in the following example:

package main import ( "fmt" "log" "github.com/upper/db/v4/adapter/postgresql" ) var settings = postgresql.ConnectionURL{ Database: "booktown", Host: "demo.upper.io", User: "demouser", Password: "demop4ss", } type Book struct { ID int64 `db:"id"` Title string `db:"title"` } func main() { sess, err := postgresql.Open(settings) if err != nil { log.Fatal("Open: ", err) } defer sess.Close() booksCollection := sess.Collection("books") // Create a result-set containing all the books in the collection. res := booksCollection.Find() // Map all items in the result-set. var books []Book if err := res.All(&books); err != nil { log.Fatal("All: ", err) } // Print all mapped items. for i := range books { fmt.Printf("book[%d]: %#v\n", i, books[i]) } }

Constraints on result-sets

The db.Cond map can be used to add constraints to result sets:

cond = db.Cond{
  "id": 36, // id equals 36
}

Note that db.Cond is a map[interface{}]interface{} type.

You can narrow down result-sets by passing db.Cond arguments to Find().

// Get items with id >= 36
cond = db.Cond{
  "id >=": 36,  // id >= 36
}
...
// Find where id >= 36
res = col.Find(cond)
...

// John Smi% is to be located.
cond = db.Cond{
  "name": "John",
  "last_name LIKE": "Smi%",
}
...
// Find where name = 'John' and last_name LIKE 'Smi%'
res = col.Find(cond)
...

// All rows that match name != "Joanna", only for SQL databases.
res = col.Find(db.Cond{"name != ?": "Joanna"})

// Same as above, but shorter.
res = col.Find(db.Cond{"name !=": "Joanna"})

db.Cond can also be used to express conditions that require special escaping or custom operators:

// "id" IN (1, 2, 3, 4)
res = col.Find(db.Cond{"id": []int{1, 2, 3, 4}})
// or...
res = col.Find(db.Cond{"id": db.In(1, 2, 3, 4)})

// "id" NOT IN (1, 2, 3, 4)
res = col.Find(db.Cond{"id NOT IN": []int{1, 2, 3, 4}})
// or...
res = col.Find(db.Cond{"id": db.NotIn(1, 2, 3, 4)})

// "last_name" IS NULL
res = col.Find(db.Cond{"last_name": nil})
// or...
res = col.Find(db.Cond{"id": db.IsNull()})

// "last_name" IS NOT NULL
res = col.Find(db.Cond{"last_name IS NOT": nil})
// or...
res = col.Find(db.Cond{"id": db.IsNotNull()})

// "last_name" LIKE "Smi%"
res = col.Find(db.Cond{"last_name LIKE": "Smi%"})
// or...
res = col.Find(db.Cond{"id": db.Like('Smi%')})

Constraints can also be composed using db.Or() or db.And():

// The item to be retrieved has a name with value "John" or "Jhon".
cond = db.Or(
  db.Cond{"name": "John"},
  db.Cond{"name": "Jhon"},
)
...

res = col.Find(cond)
...

// The ages to be retrieved can range from 22 to 27.
cond db.And(
  db.Cond{"age >=": 22},
  db.Cond{"age <=": 27},
)
...

res = col.Find(cond)
...

Nesting values is another option:

// (age > 21 AND age < 28) AND (name = "Joanna" OR name = "John" OR name = "Jhon")
cond = db.And(
  db.And( // The result set will cover ages from 22 to 27
    db.Cond{"age >": 21},
    db.Cond{"age <": 28},
  ),
  db.Or( // along with the names Joanna, John, or Jhon.
    db.Cond{"name": "Joanna"},
    db.Cond{"name": "John"},
    db.Cond{"name": "Jhon"},
  ),
)
...

res = col.Find(cond)
...

When using SQL adapters, conditions can also be expressed in string form, the first argument to Find() is a string that is followed by a list of arguments:

// These lines are equivalent.
res = col.Find("id = ?", 5)
res = col.Find("id", 5) // Means equality by default
res = col.Find("id", db.Eq(5))

// These as well.
res = col.Find("id > ?", 5)
res = col.Find("id >", 5) // Explicitly using the > comparison operator.
res = col.Find("id", db.Gt(5))

// The placeholder can be omitted when we only have one argument at the end
// of the statement.
res = col.Find("id IN ?", []int{1, 2, 3, 4})
res = col.Find("id IN", []int{1, 2, 3, 4})

// We can't omit placeholders if the argument is not at the end or when we
// expect more than one argument.
res = col.Find("id = ?::integer", "23")

// You can express complex statements as well.
var pattern string = ...
res = col.Find("MATCH(name) AGAINST(? IN BOOLEAN MODE)", pattern)

The ? symbol represents a placeholder for an argument that needs to be properly escaped, there's no need to provide numbered placeholders like $1, $2 as ? placeholders will be automatically transformed to the format the database driver expects before building a query.

Results Limit and Order

You can determine the number of items you want to go through using Offset() and Limit():

// Create a result-set
res = col.Find(...)
...

// Adjust the result-set so it will consist of 8 items and skip the first 2 rows.
res = res.Offset(2).Limit(8)
...

// Map all results into the accounts slice
err = res.All(&accounts)
...

Results can also be sorted according to a given value with OrderBy():

// Create a result-set
res := col.Find(...)
...

// Set descending order by `last_name` and map results into the accounts slice
err = res.OrderBy("-last_name").All(&accounts)
...

The total number of items in a result set can be calculated with Count():

res = col.Find(...)
...

count, err = res.Count()
...

fmt.Printf("There are %d items in the result set", count)

Limit(), Offset(), and OrderBy() affect exclusively the All() and One() methods. See all db.Result methods.

Mapping large result sets

If your result-set is too large for being just dumped into an slice without wasting a lot of memory, you can also fetch items one by one using Next() on the result-set:

res := res.Find()

var customer Customer
for res.Next(&customer) {
  log.Printf("%d: %s, %s\n", customer.ID, customer.LastName, customer.FirstName)
}

When using Next() you are the only one that knows when you're done reading the result set (unlike with All() or One()), so you'll have to Close() the result set manually after finishing using it.

res := res.Find()
defer res.Close()

See the following example with Find() and Next():

package main import ( "fmt" "log" "github.com/upper/db/v4/adapter/postgresql" ) var settings = postgresql.ConnectionURL{ Database: "booktown", Host: "demo.upper.io", User: "demouser", Password: "demop4ss", } // Customer represents a customer. type Customer struct { ID uint `db:"id"` FirstName string `db:"first_name"` LastName string `db:"last_name"` } func main() { sess, err := postgresql.Open(settings) if err != nil { log.Fatal(err) } defer sess.Close() res := sess.Collection("customers").Find().OrderBy("last_name") defer res.Close() // Make sure to close the result set. fmt.Println("Our customers:") var customer Customer // Use Next to iterate through all items on the result-set one by one. for res.Next(&customer) { fmt.Printf("%d:\t%q, %q\n", customer.ID, customer.LastName, customer.FirstName) } }

There is no need to Close() the result set when using All() or One as it's closed automatically.

Counting elements on a result set

Use the Count() method on a result set to count the number of elements on it:

res = col.Find(cond)
...

total, err := res.Count()
...

Insert

Use the Insert() method on a collection reference to insert an new item, just pass a struct value:

account := Account{
  Name:     "Eliza",
  LastName: "Smith",
  ...
}

_, err := col.Insert(account)
...

You can also use maps to insert new items:

_, err := col.Insert(map[string]interface{}{
  "name":      "Elizabeth",
  "last_name": "Smith",
  ...,
})
...

If the table or collection is set to generate a unique ID for every inserted item, that ID will be returned by Insert as a db.InsertResult value:

res, err := col.Insert(account)
...

log.Printf("Created element with ID %v", res.ID())

Keep in mind that some databases won't work correctly if they're provided with values for auto-generated fields, even if those fields have are zero values. Use omitempty to skip those fields completely:

type Account struct {
  ID uint64 `db:"id,omitempty"`
  ...
  CreatedAt *time.Time `db:"created_at,omitempty"`
  UpdatedAt *time.Time `db:"updated_at,omitempty"`
}

If your collection has an auto-generated ID and that ID is set as primary key, then you may use InsertReturning(). The InsertReturning() method takes a pointer to struct or map, inserts it into a collection and then fetches it from the collection again, all on the same transaction. This makes it possible to update the Go value with auto-generated fields, like timestamps or IDs:

err := col.InsertReturning(&account)
...

log.Printf("Account: %#v", account)

Inserting elements with the SQL builder

Use InsertInto on a session to insert a new item using the SQL builder:

// INSERT INTO people COLUMNS(name) VALUES('John')
q = sess.SQL().
  InsertInto("people").
  Columns("name").
  Values("John")

res, err := q.Exec() // res is a sql.Result
...

This SQLish syntax is only available on SQL adapters. See INSERT statement.

Update

You can update all rows on a result-set with the Update() method.

var account Account
res = col.Find("id", 5) // WHERE id = 5

// Populate account
err = res.One(&account)
...

// Change something
account.Name = "New name"
...

// Persist the change
err = res.Update(&account)
...

Update() affects all elements that match the conditions given to Find(), whether it is just one or many elements.

It is not necessary to pull the element before updating it, this would work as well:

res = col.Find("id", 5) // WHERE id = 5
...

err = res.Update(Account{
  Name: "New name",
})
...

Please note that all the struct fields without a value will be sent to the database as if they were empty. If you rather skip empty fields remember to use the omitempty option on them.

type Account struct {
  ID uint `db:"id,omitempty"`
}

You can also use maps to define an update:

res = col.Find("id", 5)
...

err = res.Update(map[string]interface{}{
  "last_login": time.Now(),
})
...

that gives you total control on which values are going to be updated.

Updating with the SQL builder

This SQLish syntax is only available on SQL adapters. See UPDATE statement.

q = sess.SQL().
  Update("people").Set("name", "John").Where("id = ?", 5)

res, err = q.Exec()
...

Delete

Use Delete() on a result set to remove all the elements on the result-set.

// Delete elements in `col` with id equals 4
res = col.Find("id", 4)
err = res.Delete()
...

// Delete elements in `col` with id greater than 8
res = col.Find("id >", 8)
err = res.Delete()
...

// Delete items in `col` with id 1 or 2 or 3 or 4
res = col.Find("id IN", []int{1, 2, 3, 4})
err = res.Delete()
...

Deleting with the SQL builder

This SQLish syntax is only available on SQL adapters. See DELETE statement.

q = sess.SQL().
  DeleteFrom("accounts").Where("id", 5)

res, err = q.Exec()
...

SQL builder

The Find() method on a collection provides a compatibility layer between SQL and NoSQL databases, but that might feel short in some situations. That's the reason why SQL adapters also provide a powerful SQL query builder.

This is how you would create a query reference using the SQL builder on a session:

q := sess.SQL().
  SelectAllFrom("accounts")
...

q := sess.SQL().
  Select("id", "last_name").From("accounts")
...

q := sess.SQL().
  SelectAllFrom("accounts").Where("last_name LIKE ?", "Smi%")
...

A query reference also provides the All() and One() methods from Result:

var accounts []Account
err = q.All(&accounts)
...

Using the query builder you can express simple queries:

q = sess.SQL().
  Select("id", "name").From("accounts").
  Where("last_name = ?", "Smith").
  OrderBy("name").Limit(10)

But even SQL-specific features, like joins, are supported (still depends on the database, though):

q = sess.SQL().
  Select("a.name").From("accounts AS a").
  Join("profiles AS p").
  On("p.account_id = a.id")

q = sess.SQL().
  Select("name").From("accounts").
  Join("owners").
  Using("employee_id")

Sometimes the builder won't be able to represent complex queries, if this happens it may be more effective to use plain SQL:

rows, err = sess.SQL().
  Query(`SELECT * FROM accounts WHERE id = ?`, 5)
...

row, err = sess.SQL().
  QueryRow(`SELECT * FROM accounts WHERE id = ? LIMIT ?`, 5, 1)
...

res, err = sess.SQL().
  Exec(`DELETE FROM accounts WHERE id = ?`, 5)
...

Mapping results from raw queries is also straightforward:

rows, err = sess.SQL().
  Query(`SELECT * FROM accounts WHERE last_name = ?`, "Smith")
...

var accounts []Account
iter := sess.SQL().NewIterator(rows)
iter.All(&accounts)
...

Take the upper/db tour

To get the full picture on how to perform all CRUD tasks (starting right from the installation and setup steps), take the upper/.db tour.