Multiple Data Sources

Most applications only ever talk to one database: the primary data source, injected everywhere as orm.DB. This page is for the rest — reporting warehouses, per-tenant databases, legacy systems you read from but do not own — reached through datasource.Registry.

Primary vs Additional Sources

The primary source is declared under vef.data_sources.primary in TOML. It is mandatory, it is the source exposed framework-wide as orm.DB, and it cannot be mutated through the dynamic registry API — Register, Update, and Unregister all reject datasource.PrimaryName ("primary") with datasource.ErrPrimaryReserved.

Every other source is "additional": either declared statically in TOML under a different name, or registered dynamically at runtime. Reach an additional source through datasource.Registry, injected wherever you need it.

Internal framework modules — CRUD, approval, storage, event inbox/outbox, schema reflection — all operate on the primary source only. Reaching an additional source, and deciding what to do with it, is an application-level concern.

Static Sources: TOML

The simplest way to add a source is another vef.data_sources.<name> table, alongside primary:

[vef.data_sources.primary]
type = "postgres"
host = "127.0.0.1"
port = 5432
user = "postgres"
password = "postgres"
database = "my_app"
schema = "public"

[vef.data_sources.analytics]
type = "sqlite"
path = "./analytics.db"

Every entry uses the same config.DataSourceConfig shape:

Field	Type	Meaning
type	postgres | mysql | sqlite	database kind (oracle and sqlserver constants exist but are not implemented yet)
host	string	network database host
port	uint16	network database port
user	string	database username
password	string	database password
database	string	database name
schema	string	schema name for drivers that support schemas
path	string	SQLite file path
enable_sql_guard	bool	enables the SQL guard for raw SQL surfaces
ssl_mode	disable | require | verify-ca | verify-full	TLS posture for network dialects; defaults to disable
ssl_root_cert	string	optional PEM path for verify-ca / verify-full

Every non-primary entry under vef.data_sources is registered into datasource.Registry under its map key before the application starts serving requests. See Configuration Reference for the full field list.

Injecting The Registry

datasource.Registry is available in the FX container everywhere. Inject it directly:

package report

import (
	"context"

	"github.com/coldsmirk/vef-framework-go/datasource"
)

type Service struct {
	sources datasource.Registry
}

func NewService(sources datasource.Registry) *Service {
	return &Service{sources: sources}
}

func (s *Service) RunReport(ctx context.Context) error {
	analytics, err := s.sources.Get("analytics")
	if err != nil {
		return err
	}

	var count int
	return analytics.NewSelect().
		ColumnExpr("count(*)").
		Table("events").
		Scan(ctx, &count)
}

Get returns an orm.DB, so it exposes the same query-building API as the primary source (NewSelect, NewInsert, NewRaw, and so on) — see Query Builder. Unknown or unregistered names return datasource.ErrNotFound. sources.Primary() returns the same orm.DB you would get from injecting orm.DB directly; it never errors.

datasource.Registry is also a built-in API handler parameter — you can request it directly as a resource handler parameter alongside orm.DB and fiber.Ctx — see Custom Handlers.

Runtime Sources: datasource.Provider

For sources that are not known at deploy time — for example, a tenant table in the primary database whose rows describe additional databases — implement datasource.Provider:

type Provider interface {
	Name() string
	Load(ctx context.Context) ([]Spec, error)
}

type Spec struct {
	Name   string
	Config config.DataSourceConfig
}

The framework calls Load once during startup, after the primary and static TOML sources are already registered, and Registers every returned Spec. A name collision with TOML or another provider fails boot. Provider.Name only labels the provider in diagnostics — it is not the data source name.

Register the provider with vef.ProvideDataSourceProvider:

func NewTenantSourceProvider(primary orm.DB) datasource.Provider {
	return &tenantSourceProvider{primary: primary}
}

// in your fx.Module:
vef.ProvideDataSourceProvider(NewTenantSourceProvider)

Provider order across multiple registered providers is undefined, so specs from different providers must not collide on name.

Runtime Sources: Direct Register

Outside of the startup Provider hook — for example, from an admin endpoint that lets an operator add a data source on demand — call Registry.Register directly:

db, err := sources.Register(ctx, "tenant-42", config.DataSourceConfig{
	Kind:     config.Postgres,
	Host:     "tenant-42.internal",
	Port:     5432,
	User:     "app",
	Password: pw,
	Database: "tenant_42",
})

Register opens and pings the new connection before inserting it; on any conflict (datasource.ErrExists for a duplicate name, datasource.ErrPrimaryReserved for "primary", datasource.ErrNameInvalid for an empty or whitespace/control-character name) the freshly opened connection is closed and nothing is inserted. Register never closes an existing connection, so it takes no options.

The Registry Surface

Method	Contract
Primary()	The primary orm.DB. Equivalent to Get(datasource.PrimaryName) but never errors.
Get(name)	The registered orm.DB. Returns datasource.ErrNotFound for an unregistered or since-unregistered name.
Has(name)	Reports whether name is currently registered and not closed.
Names()	Every registered name, including primary, in stable lexical order.
Kind(name)	The config.DBKind for name. Same not-found semantics as Get.
Register(ctx, name, cfg)	Opens and pings a new non-primary source, then inserts it.
Update(ctx, name, cfg, opts...)	Atomically swaps the connection for an existing source. The old pool is closed asynchronously.
Unregister(ctx, name, opts...)	Removes a non-primary source. The old pool is closed asynchronously.
Reconcile(ctx, specs, opts...)	Drives the registry toward a desired set of non-primary sources in one call.
TestConnection(ctx, cfg)	Opens a throwaway connection, verifies it, closes it. Never mutates the registry.
HealthCheck(ctx)	Pings every registered source in parallel; returns a name -> error map.

All read methods (Get, Has, Names, Kind, Primary) are safe for concurrent use. Register, Update, and Unregister mutate the registry atomically.

Reconciling A Desired Set

When your source list is derived from an external table (the same tenant-table scenario as the Provider example), periodic drift between that table and the registry is common: rows get added, updated, or deleted between application restarts. Reconcile closes that gap in one call, without you hand-rolling the diff:

report, err := sources.Reconcile(ctx, specs)

Given a desired []datasource.Spec, Reconcile computes three buckets and drives the registry toward them:

• a spec with no matching registry entry → Register
• a spec whose config differs from the current entry → Update
• a registry entry with no matching spec → Unregister

Specs referencing the primary name are ignored. Per-name failures are collected in ReconcileReport.Errors (keyed by name) without aborting the rest of the batch — one bad config in a batch of ten does not block the other nine. Reconciles are serialized: two ticks of a refresher job (typically a cron job calling Reconcile on a schedule) can never interleave and race each other. Direct Register / Update / Unregister calls, however, are not synchronized against a running Reconcile.

Use datasource.WithReconcileDryRun() to compute the report without opening or closing anything — useful for previewing what a refresher job would do:

preview, _ := sources.Reconcile(ctx, specs, datasource.WithReconcileDryRun())

Updating And Removing Sources

Update and Unregister are the two operations that close an existing connection, and both accept datasource.RegisterOption. By default the replaced or removed pool closes immediately on a background goroutine; WithCloseGrace(d) delays that close so in-flight queries have time to drain:

_, err := sources.Update(ctx, "analytics", newCfg, datasource.WithCloseGrace(10*time.Second))

err := sources.Unregister(ctx, "analytics", datasource.WithCloseGrace(10*time.Second))

Either way, once the call returns, Get("analytics") reflects the new state immediately (the new config for Update, datasource.ErrNotFound for Unregister) — the grace period only affects when the old underlying *sql.DB closes, so a caller that already holds an orm.DB reference from before the swap can finish its in-flight queries.

Testing And Health-Checking Connections

TestConnection is a pure connectivity probe: it opens a throwaway connection from a candidate config, confirms it by querying the server version, and closes it — it never touches the registry. It is the natural backend for a "test connection" button in an admin UI, run before calling Register or Update:

info, err := sources.TestConnection(ctx, candidateCfg)
if err != nil {
	// unreachable or unusable
}
// info.Version, e.g. "PostgreSQL 16.2 on x86_64-pc-linux-gnu"

HealthCheck instead pings every currently registered source (including primary) in parallel and returns a name -> error map, useful for a liveness/readiness endpoint that needs to see every data source at once.

Constraints To Keep In Mind

• Internal modules are primary-only. CRUD, approval, storage, event inbox/outbox, and schema reflection all read and write the primary source. Additional sources are never touched by framework internals — only by your own code.
• Cross-source transactions are not supported. orm.DB.RunInTx opens a transaction against a single source. If you publish an event with event.WithTx(tx), tx must come from a transaction opened on the primary source — see Transactions.
• Reconcile only manages non-primary sources. Specs that reference datasource.PrimaryName are silently ignored, so a Provider or reconcile job can safely include the primary name in its input without risking a boot failure.

Next Step

For the model and query-building side of things once you have an orm.DB from Get or Primary, see Query Builder and Transactions. For every other framework extension point, including vef.ProvideDataSourceProvider, see Extension Points.