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zdb provides a nice API to interact with SQL databases in Go.

Features:

  • Nice API with debugging and testing features.
  • Easier to wrap databases for logging, metrics, etc.
  • Templating in queries.
  • Run queries from filesystem.
  • Deals with some SQL interoperability issues.
  • Basic migrations.

PostgreSQL, SQLite, and MariaDB are supported, but MariaDB support is experimental and not thoroughly tested. Oracle MySQL is not supported as it's lacking some features.

This requires the following versions because it uses some features introduced in those versions:

  • SQLite 3.35 (go-sqlite3 v1.14.8)
  • PostgreSQL 12.0
  • MariaDB 10.5

To avoid confusion it gives an error when connecting if an older version is used. This also requires Go 1.16 or newer.

Full reference documentation: https://godocs.io/zgo.at/zdb

Table of contents for this README:

Usage

Connecting

You first need to register a driver similar to how you register a driver for database/sql; several drivers are available:

  • zgo.at/drivers/zdb-pq
  • zgo.at/drivers/zdb-mysql
  • zgo.at/drivers/zdb-go-sqlite3

Simply importing this package is enough; e.g.:

import _ "zgo.at/zdb-pq"

Connect() opens a new connection, runs migrations, and/or creates a database if it doesn't exist yet. A basic example:

db, err := zdb.Connect(zdb.ConnectOptions{
    Connect: "sqlite3+:memory:",
})
if err != nil {
    log.Fatal(err)
}
defer db.Close()

Connect is a connection string prefixed with either the database engine (e.g. "postgresql") or the driver name (e.g. "pq")`. Further details on the connection string depends on the driver.

Schema creation and migrations is covered in Schema creation and migrations below.

zdb.DB and context

There are two ways to use zdb:

  • The methods on the zdb.DB interface.
  • The top-level zdb.* functions, which accept a context with a zdb.DB value on it.

Both are exactly identical, and there is no real difference. Personally I think that using zdb.Get(ctx, ...) is a lot easier, but some people are against storing the database connection on the context as matter of religion – I don't really see the problem and it makes a number of things easier. At any rate, you can use either according to your faith.

You can create a context with zdb.WithDB():

db, _ := zdb.Connect(..)
ctx := zdb.WithDB(context.Background(), db)
zdb.Get(ctx, `select 1`)

But as mentioned, you don't need to use the context, the following is identical and the context is just used for cancellation:

ctx := context.Background()
db.Get(ctx, `select 1`)

I will mostly use the zdb.* functions in this documentation.

You can use zdb.GetDB() or zdb.MustGetDB() to get the zdb.DB back, but this should rarely be needed.

Running queries

The query methods are:

Get(..)             Run a query and get a single row.
Select(..)          Run a query and get multiple rows.
Exec(..)            Execute a query without returning the result.
NumRows(..)         Run a query and return the number of affected rows.
InsertID(..)        Run a query and return the last insert ID.
Query(..)           Select multiple rows, but don't immediatly load them.

Most of these work as you would expect, and similar to database/sql and sqlx. The main difference is that Exec() doesn't return an sql.Result and that NumRows() and InsertID() exist for this use case.

You can use ?, $n, or names parameters; these are all identical and work on any database:

zdb.Exec(ctx, `insert into test (value) values (?)`, "hello")
zdb.Exec(ctx, `insert into test (value) values ($1)`, "hello")
zdb.Exec(ctx, `insert into test (value) values (:value)`, zdb.P{"value": "hello"})

zdb.P is just a map[string]interface{}, except shorter. The "P" is for "Parameters".

You can pass multiple structs and/or maps with named parameters:

err = zdb.Exec(ctx, `info into test (a, b) (:a, :b)`,
    zdb.P{"A": "hello"},
    struct{B int}{42})

Get(), Select(), and Query() can scan the results in to a struct or map; see the function documentation for details on the exact rules.

Simple conditionals

There is a mini template language for conditionals; this only works if you're using named parameters:

var values []string
err := zdb.Select(ctx, &values, `
    select * from test
    where
        value = :val {{:val2 and value not like :val2}}
`, zdb.P{
    "val":  "hello",
    "val2": "%world",
})

The text between {{:param ... }} will be omitted if param is false or the type's zero value. End with the parameter name with ! to invert the match: {{:param! ... }}.

I find this is a fairly nice middle ground between writing plain SQL queries and using more complex query builder DSLs.

Templates

For more complex use cases you can use text/template; this only works for queries loaded from the filesystem, and the filenames need to end with .gotxt.

The following functions are available:

sqlite "str"        Include str only for SQLite.
psql   "str"        Include str only for PostgreSQL
mysql  "str"        Include str only for MySQL/MariaDB.

auto_increment      Return the column type for an auto-increment column.

jsonb               Return the column type for a JSON column.
blob                Return the column type for a binary data column.

You can set additional functions (or override any of the above) by adding functions to zdb.TemplateFuncMap.

Queries from filesystem

Queries are loaded from the filesystem if the query starts with load::

var values []string
err := zdb.Select(ctx, &values, `load:find-site`, zdb.P{
    "name": "hello",
})

The special prefix load:[filename] loads a query from the db/query/ directory. You can use zdb.Load() to only read a query from the filesystem.

Comments in the form of -- at the start of the line only are stripped. This makes queries a bit less noisy in query logs and the like.

This requires the Files parameter in ConnectOptions to be set; e.g.

zdb.Connect(zdb.ConnectOptions{
    Connect: "...",
    Files:   os.DirFS("db"),
})

You can also use embeded files here.

Transactions

zdb.TX(func(..) { }) runs the function in a transaction:

err := zdb.TX(ctx, func(ctx context.Context) error {
    err := zdb.Exec(ctx, ..)
    if err != nil {
        return err
    }

    // ... more queries
})
if err != nil {
    log.Fatal(err)
}

The transaction will be rolled back if an error is returned, or committed if it doesn't. This can be nested, but will start only one transaction and will only be committed after the outermost transaction finishes.

You can also start a transaction with zdb.Begin(), but I find the TX() wrapper more useful in almost all cases:

txctx, tx, err := zdb.Begin(ctx)
if err != nil {
    return err
}
defer tx.Rollback()

// Do stuff with tx...

err := tx.Commit()
if err != nil {
    return err
}

Schema creation and migrations

If Create is set in zdb.Connect(), it will try to:

  1. Create the database if it does not yet exist.
  2. Tun the schema setup file if there are no tables yet and the file exists; this requires the Files parameter to be set.

The schemas to set up the database should be in /schema-{dialect}.sql, /schema.gotxt, or /schema.sql. Files are tried in that order. The {dialect} is sqlite3, postgres, or mariadb and only needed if you need to vary something by SQL engine: otherwise it will just load the generic file. You can also use templating with .gotxt files, as documented above.

Migrations are loaded from /migrate/foo-{dialect}.sql, /migrate/foo.gotxt, or /migrate/foo.sql. Migrations are always run in lexical order, so you probably want to prefix them with the date, and maybe a sequence number for the day in case you have multiple migrations on the same day (e.g. 2021-06-18-1-name.sql). It uses a version table to keep track of which migrations were already run (will be created automatically if it doesn't exist).

This isn't really intended to solve every possible use case for database migrations, but it should be enough for many use cases, and for more advanced things you can use one of several dedicated packages.

You can also pass GoMigrations in zdb.Connect() to run Go code as migrations. This is sometimes more convenient if you need to do some complex processing.

It's okay if directories are missing; e.g. no migrate directory simply means that it won't attempt to run migrations – you don't need to use all features.

Bulk insert

BulkInsert makes it easier to bulk insert values:

ins := zdb.NewBulkInsert(ctx, "table", []string{"col1", "col2", "col3"})
for _, v := range listOfValues {
    ins.Values(v.Col1, v.Col2, v.Col3)
}
err := ins.Finish()

This won't naïvely group everything in one query; after more than 998 parameters it will construct an SQL query and send it to the server. 998 was chosen because that's the default SQLite limit, and you probably won't get much benefit from larger inserts anyway.

You get the error(s) back with Finish().

Note this isn't run in a transaction by default; start a transaction yourself if you want it.

Testing and debugging

DumpArgs

zdb has a rather useful facility of "DumpArgs"; you can add it to any query method and it will "dump" information to stderr. This is really useful for quick testing/debugging:

TODO: include somewhwat realistic example here.

Testing

RunTest()              Create a temporary database and run tests.
TestQueries()          Test queries from fs.

Dump(), DumpString()   Show result of any query.
ApplyParams()          Apply parameters.

zdb.Dump() and zdb.DumpString() are two rather useful helper functions: they get the output of any SQL query in a table, similar to what you get on the sqlite3 or psql commandline. This is rather useful for debugging and tests:

want := `
    site    day                            browser  version  count   count_unique  event
    1       2019-08-31 00:00:00 +0000 UTC  Firefox  68.0     1       0             0`

out := zdb.DumpString(ctx, `select * from table`)

if d := ztest.Diff(out, want, ztest.DiffNormalizeWhitespace); d != "" {
    t.Error(d)
}

This will panic() on errors. Again, it's only intended for debugging and tests, and omitting error returns makes it a bit smoother to use.

The zdb.ApplyParams() function will replace ? and $1 with the actual values. This is intended to make copying long-ish queries to the psql CLI for additional debugging/testing easier. This is not intended for any serious use and is not safe against malicious input.

fmt.Println(zdb.ApplyParams(
    `select * from users where site=$1 and state=$2`,
    1, "active"))

// Output: select * from users where site=1 and state='active'

Database wrapping

Wrapping a database well with database/sql or sqlx is a bit tricky since you need to wrap both the actual database but also the transactions.

LogDB

Wrap the database with zdb.NewLognDB() to automatically dump the query, the results, the explain, or all of them to a writer:

db, _ := zdb.Connect(...)
logDB = zdb.NewLogDB(db, os.Stdout, zdb.DumpAll, "")

The last parameter is an optional filter:

logDB = zdb.NewExplainDB(db, os.Stdout, zdb.DumpAll, "only_if_query_matches_this_text")

This may run queries twice.

MetricsDB

Wrap the database with zdb.NewMetricsDB() to record metrics on the execution of query times. This takes a "recoder", and the Record() method is called for every query invocation.

There is a MetricsMemory, which records the metrics in the process memory. You can implement your own to send metrics to datadog or grafana or whatnot.

    db, _ := zdb.Connect(...)
    metricDB := zdb.NewMetricsDB(db, zdb.NewMetricsMemory(0))

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zdb provides a nice API to interact with SQL databases in Go

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