Add sqlc.slice() to support IN clauses in MySQL (#695)

This feature (currently MySQL-specific) allows passing in a slice to an
IN clause. Adding the new function sqlc.slice() as opposed to overloading
the parsing of "IN (?)" was chosen to guarantee backwards compatibility.

   SELECT * FROM tab WHERE col IN (sqlc.slice("go_param_name"))

This commit is based on #1312 by
Paul Cameron. I just rebased and did some cleanup.

Co-authored-by: Paul Cameron <cameronpm@gmail.com>

Author: Jille

docs/howto/select.md

@@ -185,6 +185,8 @@ func (q *Queries) GetInfoForAuthor(ctx context.Context, id int) (GetInfoForAutho
 
 ## Passing a slice as a parameter to a query
 
+### PostgreSQL
+
 In PostgreSQL,
 [ANY](https://www.postgresql.org/docs/current/functions-comparisons.html#id-1.5.8.28.16)
 allows you to check if a value exists in an array expression. Queries using ANY
@@ -262,3 +264,111 @@ func (q *Queries) ListAuthorsByIDs(ctx context.Context, ids []int) ([]Author, er
 	return items, nil
 }
 ```
+
+### MySQL
+
+MySQL differs from PostgreSQL in that placeholders must be generated based on
+the number of elements in the slice you pass in. Though trivial it is still
+something of a nuisance. The passed in slice must not be nil or empty or an
+error will be returned (ie not a panic). The placeholder insertion location is
+marked by the meta-function `sqlc.slice()` (which is similar to `sqlc.arg()`
+that you see documented under [Naming parameters](named_parameters.md)).
+
+To rephrase, the `sqlc.slice('param')` behaves identically to `sqlc.arg()` it
+terms of how it maps the explicit argument to the function signature, eg:
+
+  * `sqlc.slice('ids')` maps to `ids []GoType` in the function signature
+  * `sqlc.slice(cust_ids)` maps to `custIds []GoType` in the function signature
+    (like `sqlc.arg()`, the parameter does not have to be quoted)
+
+This feature is not compatible with `emit_prepared_queries` statement found in the
+[Configuration file](../reference/config.md).
+
+```sql
+CREATE TABLE authors (
+  id         SERIAL PRIMARY KEY,
+  bio        text   NOT NULL,
+  birth_year int    NOT NULL
+);
+
+-- name: ListAuthorsByIDs :many
+SELECT * FROM authors
+WHERE id IN (sqlc.slice('ids'));
+```
+
+The above SQL will generate the following code:
+
+```go
+package db
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"strings"
+)
+
+type Author struct {
+	ID        int
+	Bio       string
+	BirthYear int
+}
+
+type DBTX interface {
+	ExecContext(context.Context, string, ...interface{}) (sql.Result, error)
+	PrepareContext(context.Context, string) (*sql.Stmt, error)
+	QueryContext(context.Context, string, ...interface{}) (*sql.Rows, error)
+	QueryRowContext(context.Context, string, ...interface{}) *sql.Row
+}
+
+func New(db DBTX) *Queries {
+	return &Queries{db: db}
+}
+
+type Queries struct {
+	db DBTX
+}
+
+func (q *Queries) WithTx(tx *sql.Tx) *Queries {
+	return &Queries{
+		db: tx,
+	}
+}
+
+const listAuthorsByIDs = `-- name: ListAuthorsByIDs :many
+SELECT id, bio, birth_year FROM authors
+WHERE id IN (/*SLICE:ids*/?)
+`
+
+func (q *Queries) ListAuthorsByIDs(ctx context.Context, ids []int64) ([]Author, error) {
+	sql := listAuthorsByIDs
+	var queryParams []interface{}
+	if len(ids) == 0 {
+		return nil, fmt.Errorf("slice ids must have at least one element")
+	}
+	for _, v := range ids {
+		queryParams = append(queryParams, v)
+	}
+	sql = strings.Replace(sql, "/*SLICE:ids*/?", strings.Repeat(",?", len(ids))[1:], 1)
+	rows, err := q.db.QueryContext(ctx, sql, queryParams...)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []Author
+	for rows.Next() {
+		var i Author
+		if err := rows.Scan(&i.ID, &i.Bio, &i.BirthYear); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Close(); err != nil {
+		return nil, err
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+```

internal/cmd/shim.go

@@ -241,6 +241,7 @@ func pluginQueryColumn(c *compiler.Column) *plugin.Column {
 		Length:       int32(l),
 		IsNamedParam: c.IsNamedParam,
 		IsFuncCall:   c.IsFuncCall,
+		IsSqlcSlice:  c.IsSqlcSlice,
 	}
 
 	if c.Type != nil {

internal/codegen/golang/field.go

@@ -14,6 +14,7 @@ type Field struct {
 	Type    string
 	Tags    map[string]string
 	Comment string
+	Column  *plugin.Column
 }
 
 func (gf Field) Tag() string {
@@ -28,6 +29,10 @@ func (gf Field) Tag() string {
 	return strings.Join(tags, " ")
 }
 
+func (gf Field) HasSqlcSlice() bool {
+	return gf.Column.IsSqlcSlice
+}
+
 func JSONTagName(name string, settings *plugin.Settings) string {
 	style := settings.Go.JsonTagsCaseStyle
 	if style == "" || style == "none" {

internal/codegen/golang/gen.go

@@ -43,6 +43,63 @@ func (t *tmplCtx) OutputQuery(sourceName string) bool {
 	return t.SourceName == sourceName
 }
 
+func (t *tmplCtx) codegenDbarg() string {
+	if t.EmitMethodsWithDBArgument {
+		return "db DBTX, "
+	}
+	return ""
+}
+
+// Called as a global method since subtemplate queryCodeStdExec does not have
+// access to the toplevel tmplCtx
+func (t *tmplCtx) codegenEmitPreparedQueries() bool {
+	return t.EmitPreparedQueries
+}
+
+func (t *tmplCtx) codegenQueryMethod(q Query) string {
+	db := "q.db"
+	if t.EmitMethodsWithDBArgument {
+		db = "db"
+	}
+
+	switch q.Cmd {
+	case ":one":
+		if t.EmitPreparedQueries {
+			return "q.queryRow"
+		}
+		return db + ".QueryRowContext"
+
+	case ":many":
+		if t.EmitPreparedQueries {
+			return "q.query"
+		}
+		return db + ".QueryContext"
+
+	default:
+		if t.EmitPreparedQueries {
+			return "q.exec"
+		}
+		return db + ".ExecContext"
+	}
+}
+
+func (t *tmplCtx) codegenQueryRetval(q Query) (string, error) {
+	switch q.Cmd {
+	case ":one":
+		return "row :=", nil
+	case ":many":
+		return "rows, err :=", nil
+	case ":exec":
+		return "_, err :=", nil
+	case ":execrows":
+		return "result, err :=", nil
+	case ":execresult":
+		return "return", nil
+	default:
+		return "", fmt.Errorf("unhandled q.Cmd case %q", q.Cmd)
+	}
+}
+
 func Generate(ctx context.Context, req *plugin.CodeGenRequest) (*plugin.CodeGenResponse, error) {
 	enums := buildEnums(req)
 	structs := buildStructs(req)
@@ -61,24 +118,6 @@ func generate(req *plugin.CodeGenRequest, enums []Enum, structs []Struct, querie
 		Structs:  structs,
 	}
 
-	funcMap := template.FuncMap{
-		"lowerTitle": sdk.LowerTitle,
-		"comment":    sdk.DoubleSlashComment,
-		"escape":     sdk.EscapeBacktick,
-		"imports":    i.Imports,
-		"hasPrefix":  strings.HasPrefix,
-	}
-
-	tmpl := template.Must(
-		template.New("table").
-			Funcs(funcMap).
-			ParseFS(
-				templates,
-				"templates/*.tmpl",
-				"templates/*/*.tmpl",
-			),
-	)
-
 	golang := req.Settings.Go
 	tctx := tmplCtx{
 		EmitInterface:             golang.EmitInterface,
@@ -107,6 +146,31 @@ func generate(req *plugin.CodeGenRequest, enums []Enum, structs []Struct, querie
 		return nil, errors.New(":batch* commands are only supported by pgx")
 	}
 
+	funcMap := template.FuncMap{
+		"lowerTitle": sdk.LowerTitle,
+		"comment":    sdk.DoubleSlashComment,
+		"escape":     sdk.EscapeBacktick,
+		"imports":    i.Imports,
+		"hasPrefix":  strings.HasPrefix,
+
+		// These methods are Go specific, they do not belong in the codegen package
+		// (as that is language independent)
+		"dbarg":               tctx.codegenDbarg,
+		"emitPreparedQueries": tctx.codegenEmitPreparedQueries,
+		"queryMethod":         tctx.codegenQueryMethod,
+		"queryRetval":         tctx.codegenQueryRetval,
+	}
+
+	tmpl := template.Must(
+		template.New("table").
+			Funcs(funcMap).
+			ParseFS(
+				templates,
+				"templates/*.tmpl",
+				"templates/*/*.tmpl",
+			),
+	)
+
 	output := map[string]string{}
 
 	execute := func(name, templateName string) error {

internal/codegen/golang/go_type.go

@@ -37,7 +37,7 @@ func goType(req *plugin.CodeGenRequest, col *plugin.Column) string {
 		}
 	}
 	typ := goInnerType(req, col)
-	if col.IsArray {
+	if col.IsArray || col.IsSqlcSlice {
 		return "[]" + typ
 	}
 	return typ

internal/codegen/golang/imports.go

@@ -363,12 +363,24 @@ func (i *importer) queryImports(filename string) fileImports {
 		return false
 	}
 
+	// Search for sqlc.slice() calls
+	sqlcSliceScan := func() bool {
+		for _, q := range gq {
+			if q.Arg.HasSqlcSlices() {
+				return true
+			}
+		}
+		return false
+	}
+
 	if anyNonCopyFrom {
 		std["context"] = struct{}{}
 	}
 
 	sqlpkg := parseDriver(i.Settings.Go.SqlPackage)
-	if sliceScan() && !sqlpkg.IsPGX() {
+	if sqlcSliceScan() {
+		std["strings"] = struct{}{}
+	} else if sliceScan() && !sqlpkg.IsPGX() {
 		pkg[ImportSpec{Path: "github.com/lib/pq"}] = struct{}{}
 	}
 

internal/codegen/golang/query.go

@@ -15,6 +15,10 @@ type QueryValue struct {
 	Struct      *Struct
 	Typ         string
 	SQLDriver   SQLDriver
+
+	// Column is kept so late in the generation process around to differentiate
+	// between mysql slices and pg arrays
+	Column *plugin.Column
 }
 
 func (v QueryValue) EmitStruct() bool {
@@ -93,14 +97,14 @@ func (v QueryValue) Params() string {
 	}
 	var out []string
 	if v.Struct == nil {
-		if strings.HasPrefix(v.Typ, "[]") && v.Typ != "[]byte" && !v.SQLDriver.IsPGX() {
+		if !v.Column.IsSqlcSlice && strings.HasPrefix(v.Typ, "[]") && v.Typ != "[]byte" && !v.SQLDriver.IsPGX() {
 			out = append(out, "pq.Array("+v.Name+")")
 		} else {
 			out = append(out, v.Name)
 		}
 	} else {
 		for _, f := range v.Struct.Fields {
-			if strings.HasPrefix(f.Type, "[]") && f.Type != "[]byte" && !v.SQLDriver.IsPGX() {
+			if !f.HasSqlcSlice() && strings.HasPrefix(f.Type, "[]") && f.Type != "[]byte" && !v.SQLDriver.IsPGX() {
 				out = append(out, "pq.Array("+v.Name+"."+f.Name+")")
 			} else {
 				out = append(out, v.Name+"."+f.Name)
@@ -125,6 +129,20 @@ func (v QueryValue) ColumnNames() string {
 	return "[]string{" + strings.Join(escapedNames, ", ") + "}"
 }
 
+// When true, we have to build the arguments to q.db.QueryContext in addition to
+// munging the SQL
+func (v QueryValue) HasSqlcSlices() bool {
+	if v.Struct == nil {
+		return v.Column != nil && v.Column.IsSqlcSlice
+	}
+	for _, v := range v.Struct.Fields {
+		if v.Column.IsSqlcSlice {
+			return true
+		}
+	}
+	return false
+}
+
 func (v QueryValue) Scan() string {
 	var out []string
 	if v.Struct == nil {

internal/codegen/golang/result.go

@@ -168,6 +168,7 @@ func buildQueries(req *plugin.CodeGenRequest, structs []Struct) ([]Query, error)
 				Name:      paramName(p),
 				Typ:       goType(req, p.Column),
 				SQLDriver: sqlpkg,
+				Column:    p.Column,
 			}
 		} else if len(query.Params) > 1 {
 			var cols []goColumn
@@ -311,6 +312,7 @@ func columnsToStruct(req *plugin.CodeGenRequest, name string, columns []goColumn
 			DBName: colName,
 			Type:   goType(req, c.Column),
 			Tags:   tags,
+			Column: c.Column,
 		})
 		if _, found := seen[baseFieldName]; !found {
 			seen[baseFieldName] = []int{i}