Patcher

Patcher is a GO library that provides a simple way to generate and SQL patches from structs. The library was built out of the need to generate patches for a database; when a new field is added to a struct, this would result in a bunch of new if checks to be created in the codebase. This library aims to solve that problem by generating the SQL patches for you.

Usage

Basic

To use the library, you need to create a struct that represents the table you want to generate patches for. The struct should have the following tags:

• db:"column_name": This tag is used to specify the column name in the database.

Example:

package main

import (
	"encoding/json"
	"fmt"

	"github.com/jacobbrewer1/patcher"
)

type Person struct {
	ID   *int    `db:"id"`
	Name *string `db:"name"`
	Age  *int    `db:"age"`
}

type PersonWhere struct {
	ID *int `db:"id"`
}

func NewPersonWhere(id int) *PersonWhere {
	return &PersonWhere{
		ID: &id,
	}
}

func (p *PersonWhere) Where() (string, []any) {
	return "id = ?", []any{*p.ID}
}

func main() {
	const jsonStr = `{"name": "John", "age": 25}`

	person := new(Person)
	if err := json.Unmarshal([]byte(jsonStr), person); err != nil {
		panic(err)
	}

	condition := NewPersonWhere(1)

	sqlStr, args, err := patcher.GenerateSQL(
		person,
		patcher.WithTable("people"),
		patcher.WithWhere(condition),
	)
	if err != nil {
		panic(err)
	}

	fmt.Println(sqlStr)
	fmt.Println(args)
}

This will output:

UPDATE people
SET name = ?,
    age  = ?
WHERE (1 = 1)
  AND (
    id = ?
    )

with the args:

["John", 25, 1]

Struct diffs

The Patcher library has functionality where you are able to inject changes from one struct to another. This is configurable to include Zero values and Nil values if requested. Please see the example here for the detailed example. Below is an example on how you can utilize this method with the default behaviour (Please see the comment attached to the LoadDiff method for the default behaviour).

Example:

package main

import (
	"fmt"

	"github.com/jacobbrewer1/patcher"
)

type Something struct {
	Number       int
	Text         string
	PrePopulated string
	NewText      string
}

func main() {
	s := Something{
		Number:       5,
		Text:         "Hello",
		PrePopulated: "PrePopulated",
	}

	n := Something{
		Number:  6,
		Text:    "Old Text",
		NewText: "New Text",
	}

	// The patcher.LoadDiff function will apply the changes from n to s.
	if err := patcher.LoadDiff(&s, &n); err != nil {
		panic(err)
	}

	// Output:
	// 6
	// Old Text
	// PrePopulated
	// New Text
	fmt.Println(s.Number)
	fmt.Println(s.Text)
	fmt.Println(s.PrePopulated)
	fmt.Println(s.NewText)
}

If you would like to generate an update script from two structs, you can use the NewDiffSQLPatch function. This function will generate an update script from the two structs.

Example:

package main

import (
	"fmt"

	"github.com/jacobbrewer1/patcher"
)

type Something struct {
	Number       int
	Text         string
	PrePopulated string
	NewText      string
}

type SomeWhere struct {
	id int
}

func NewSomeWhere(id int) *SomeWhere {
	return &SomeWhere{id: id}
}

func (s *SomeWhere) Where() (string, []any) {
	return "id = ?", []any{s.id}
}

func main() {
	s := Something{
		Number:       5,
		Text:         "Old Text",
		PrePopulated: "PrePopulated",
		NewText:      "New Text",
	}

	n := Something{
		Number:       5,
		Text:         "Old Text",
		PrePopulated: "PrePopulatedDifferent",
		NewText:      "New Text",
	}

	wherer := NewSomeWhere(5)

	// The patcher.LoadDiff function will apply the changes from n to s.
	patch, err := patcher.NewDiffSQLPatch(
		&s,
		&n,
		patcher.WithTable("table_name"),
		patcher.WithWhere(wherer),
	)
	if err != nil {
		panic(err)
	}

	sqlStr, sqlArgs, err := patch.GenerateSQL()
	if err != nil {
		panic(err)
	}

	fmt.Println(sqlStr)
	fmt.Println(sqlArgs)
}

This will output:

UPDATE table_name
SET pre_populated = ?
WHERE (1 = 1)
  AND (
    id = ?
    )

with the args:

["PrePopulatedDifferent", 5]

You can also take a look at the Loader examples for more examples on how to use the library for this approach.

Using OR in the where clause

If you would like to use OR in the where clause, you can apply the patcher.WhereTyper interface to your where struct. Please take a look at the example here.

Joins

To generate a join, you need to create a struct that represents the join. This struct should implement the Joiner interface.

Once you have the join struct, you can pass it to the GenerateSQL function using the WithJoin option. You can add as many of these as you would like.

Examples

You can find examples of how to use this library in the examples directory.