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Merge pull request #85 from dogmatiq/schema-functions
Add `sqlprojection.CreateSchema()` and `DropSchema()`.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,40 @@ | ||
| package sqlprojection | ||
|
|
||
| import ( | ||
| "context" | ||
| "database/sql" | ||
| ) | ||
|
|
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| // CreateSchema creates the schema elements necessary to store projections on | ||
| // the given database. | ||
| // | ||
| // If no candidate drivers are provided all built-in drivers are considered as | ||
| // candidates. | ||
| func CreateSchema(ctx context.Context, db *sql.DB, options ...Option) error { | ||
| var cs candidateSet | ||
| cs.init(db, options) | ||
|
|
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| d, err := cs.resolve(ctx) | ||
| if err != nil { | ||
| return err | ||
| } | ||
|
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| return d.CreateSchema(ctx, db) | ||
| } | ||
|
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| // DropSchema drops the schema elements necessary to store projections on the | ||
| // given database. | ||
| // | ||
| // If no candidate drivers are provided all built-in drivers are considered as | ||
| // candidates. | ||
| func DropSchema(ctx context.Context, db *sql.DB, options ...Option) error { | ||
| var cs candidateSet | ||
| cs.init(db, options) | ||
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| d, err := cs.resolve(ctx) | ||
| if err != nil { | ||
| return err | ||
| } | ||
|
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| return d.DropSchema(ctx, db) | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,122 @@ | ||
| package sqlprojection | ||
|
|
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| import ( | ||
| "context" | ||
| "database/sql" | ||
| "fmt" | ||
| "sync/atomic" | ||
|
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| "github.com/dogmatiq/cosyne" | ||
| "go.uber.org/multierr" | ||
| ) | ||
|
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| // SelectDriver returns the appropriate driver implementation to use with the | ||
| // given database from a list of candidate drivers. | ||
| func SelectDriver(ctx context.Context, db *sql.DB, candidates []Driver) (Driver, error) { | ||
| var err error | ||
|
|
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| for _, d := range candidates { | ||
| e := d.IsCompatibleWith(ctx, db) | ||
| if e == nil { | ||
| return d, nil | ||
| } | ||
|
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| err = multierr.Append(err, fmt.Errorf( | ||
| "%T is not compatible with %T: %w", | ||
| d, | ||
| db.Driver(), | ||
| e, | ||
| )) | ||
| } | ||
|
|
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| return nil, multierr.Append(err, fmt.Errorf( | ||
| "none of the candidate drivers are compatible with %T", | ||
| db.Driver(), | ||
| )) | ||
| } | ||
|
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| // An Option configures the optional behavior of an SQL projection. | ||
| type Option interface { | ||
| applyCandidateSetOption(*candidateSet) | ||
| } | ||
|
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| type adaptorOptionFunc func(*candidateSet) | ||
|
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| func (f adaptorOptionFunc) applyCandidateSetOption(s *candidateSet) { | ||
| f(s) | ||
| } | ||
|
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| // WithDriver returns an Option that forces use of a specific Driver. | ||
| // | ||
| // It takes precedence over any WithCandidateDriver() option. | ||
| func WithDriver(d Driver) Option { | ||
| return adaptorOptionFunc(func(s *candidateSet) { | ||
| s.resolved = 1 | ||
| s.candidates = []Driver{d} | ||
| }) | ||
| } | ||
|
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| // WithCandidateDrivers returns an Option that adds candidate drivers for | ||
| // selection as the driver to use. | ||
| func WithCandidateDrivers(drivers ...Driver) Option { | ||
| return adaptorOptionFunc(func(s *candidateSet) { | ||
| if s.resolved == 0 { | ||
| s.candidates = append(s.candidates, drivers...) | ||
| } | ||
| }) | ||
| } | ||
|
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| // candidateSet is a set of drivers that are candidates for use with a | ||
| // particular database. | ||
| type candidateSet struct { | ||
| m cosyne.Mutex | ||
| resolved uint32 | ||
| db *sql.DB | ||
| candidates []Driver | ||
| } | ||
|
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| // init sets up the candidate set. | ||
| // | ||
| // If options is empty the default options are applied. | ||
| func (s *candidateSet) init(db *sql.DB, options []Option) { | ||
| s.db = db | ||
|
|
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| if len(options) == 0 { | ||
| options = []Option{ | ||
| WithCandidateDrivers(BuiltInDrivers()...), | ||
| } | ||
| } | ||
|
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| for _, opt := range options { | ||
| opt.applyCandidateSetOption(s) | ||
| } | ||
| } | ||
|
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| // resolve selects the appropriate driver from the candidates. | ||
| func (s *candidateSet) resolve(ctx context.Context) (Driver, error) { | ||
| if atomic.LoadUint32(&s.resolved) == 0 { | ||
| // If the resolved flag is 0 then a.selected has not been populated yet. | ||
| // We acquire the mutex to ensure we're the only goroutine attempting | ||
| // selection. | ||
| if err := s.m.Lock(ctx); err != nil { | ||
| return nil, err | ||
| } | ||
| defer s.m.Unlock() | ||
|
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| // Ensure that no another goroutine selected the driver while we were | ||
| // waiting to acquire the mutex. | ||
| if atomic.LoadUint32(&s.resolved) == 0 { | ||
| // If not, it's our turn to try selection. | ||
| d, err := SelectDriver(ctx, s.db, s.candidates) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
|
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| s.db = nil | ||
| s.candidates = []Driver{d} | ||
| atomic.StoreUint32(&s.resolved, 1) | ||
| } | ||
| } | ||
|
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| return s.candidates[0], nil | ||
| } |