refactor: replace per-dialect extractors with generic extractor

Collapse the mssql- and postgres-specific extractors into a single generic implementation driven by the DB dialect interface.

internal/app/db-wrapper/db_dialects/main.go

@@ -0,0 +1,7 @@
+package db_dialects
+
+const (
+	SqlServer string = "sqlserver"
+	Postgres  string = "postgres"
+	Null      string = "null"
+)

internal/app/db-wrapper/mssql.go

@@ -4,13 +4,15 @@ import (
 	"context"
 	"database/sql"
 	"fmt"
+	"strings"
 
+	dbdialects "git.ksdemosapps.com/kylesoda/go-migrate/internal/app/db-wrapper/db_dialects"
 	mssql "github.com/microsoft/go-mssqldb"
 )
 
 func init() {
-	Register("sqlserver", func() DbWrapper {
-		return &mssqlDbWrapper{dialect: "sqlserver"}
+	Register(dbdialects.SqlServer, func() DbWrapper {
+		return &mssqlDbWrapper{dialect: dbdialects.SqlServer}
 	})
 }
 
@@ -174,3 +176,72 @@ func (mw *mssqlDbWrapper) SaveMassive(ctx context.Context, schema string, table
 
 	return rowsAffected, nil
 }
+
+func (mw *mssqlDbWrapper) QueryFromObject(ctx context.Context, q ExtractionQuery) (RowsResult, error) {
+	var sbQuery strings.Builder
+
+	sbQuery.WriteString("SELECT ")
+
+	if len(q.columns) == 0 {
+		sbQuery.WriteString("*")
+	} else {
+		for i, col := range q.columns {
+			fmt.Fprintf(&sbQuery, "[%s]", col.Name())
+
+			switch col.Type() {
+			case "GEOMETRY":
+				fmt.Fprintf(&sbQuery, ".STAsBinary() AS [%s]", col.Name())
+			}
+
+			if i < len(q.columns)-1 {
+				sbQuery.WriteString(", ")
+			}
+		}
+	}
+
+	fmt.Fprintf(&sbQuery, " FROM [%s].[%s]", q.Schema, q.Table)
+
+	if q.LowerLimit.IsValid || q.UpperLimit.IsValid {
+		sbQuery.WriteString(" WHERE ")
+
+		if q.LowerLimit.IsValid {
+			fmt.Fprintf(&sbQuery, "[%s]", q.PrimaryKey)
+			if q.LowerLimit.IsInclusive {
+				sbQuery.WriteString(" >=")
+			} else {
+				sbQuery.WriteString(" >")
+			}
+			sbQuery.WriteString(" @min")
+		}
+
+		if q.LowerLimit.IsValid && q.UpperLimit.IsValid {
+			sbQuery.WriteString(" AND ")
+		}
+
+		if q.UpperLimit.IsValid {
+			fmt.Fprintf(&sbQuery, "[%s]", q.PrimaryKey)
+			if q.UpperLimit.IsInclusive {
+				sbQuery.WriteString(" <=")
+			} else {
+				sbQuery.WriteString(" <")
+			}
+			sbQuery.WriteString(" @max")
+		}
+	}
+
+	fmt.Fprintf(&sbQuery, " ORDER BY [%s] ASC", q.PrimaryKey)
+
+	queryString := sbQuery.String()
+
+	var queryArgs []any
+
+	if q.LowerLimit.IsValid {
+		queryArgs = append(queryArgs, sql.Named("min", q.LowerLimit.Value))
+	}
+
+	if q.UpperLimit.IsValid {
+		queryArgs = append(queryArgs, sql.Named("max", q.UpperLimit.Value))
+	}
+
+	return mw.Query(ctx, queryString, queryArgs...)
+}

internal/app/db-wrapper/postgres.go

@@ -3,14 +3,17 @@ package dbwrapper
 import (
 	"context"
 	"errors"
+	"fmt"
+	"strings"
 
+	dbdialects "git.ksdemosapps.com/kylesoda/go-migrate/internal/app/db-wrapper/db_dialects"
 	"github.com/jackc/pgx/v5"
 	"github.com/jackc/pgx/v5/pgxpool"
 )
 
 func init() {
-	Register("postgres", func() DbWrapper {
-		return &postgresDbWrapper{dialect: "postgres"}
+	Register(dbdialects.Postgres, func() DbWrapper {
+		return &postgresDbWrapper{dialect: dbdialects.Postgres}
 	})
 }
 
@@ -126,3 +129,75 @@ func (pw *postgresDbWrapper) SaveMassive(ctx context.Context, schema string, tab
 
 	return affectedRows, nil
 }
+
+func (pw *postgresDbWrapper) QueryFromObject(ctx context.Context, q ExtractionQuery) (RowsResult, error) {
+	var sbQuery strings.Builder
+
+	sbQuery.WriteString("SELECT ")
+
+	if len(q.columns) == 0 {
+		sbQuery.WriteString("*")
+	} else {
+		for i, col := range q.columns {
+			switch col.Type() {
+			case "GEOMETRY":
+				fmt.Fprintf(&sbQuery, `ST_AsEWKB("%s") AS "%s"`, col.Name(), col.Name())
+			default:
+				fmt.Fprintf(&sbQuery, `"%s"`, col.Name())
+			}
+
+			if i < len(q.columns)-1 {
+				sbQuery.WriteString(", ")
+			}
+		}
+	}
+
+	fmt.Fprintf(&sbQuery, ` FROM "%s"."%s"`, q.Schema, q.Table)
+
+	if q.LowerLimit.IsValid || q.UpperLimit.IsValid {
+		sbQuery.WriteString(" WHERE ")
+		paramIdx := 1
+
+		if q.LowerLimit.IsValid {
+			fmt.Fprintf(&sbQuery, `"%s"`, q.PrimaryKey)
+			if q.LowerLimit.IsInclusive {
+				sbQuery.WriteString(" >=")
+			} else {
+				sbQuery.WriteString(" >")
+			}
+			fmt.Fprintf(&sbQuery, " $%d", paramIdx)
+			paramIdx++
+		}
+
+		if q.LowerLimit.IsValid && q.UpperLimit.IsValid {
+			sbQuery.WriteString(" AND ")
+		}
+
+		if q.UpperLimit.IsValid {
+			fmt.Fprintf(&sbQuery, `"%s"`, q.PrimaryKey)
+			if q.UpperLimit.IsInclusive {
+				sbQuery.WriteString(" <=")
+			} else {
+				sbQuery.WriteString(" <")
+			}
+			fmt.Fprintf(&sbQuery, " $%d", paramIdx)
+			paramIdx++
+		}
+	}
+
+	fmt.Fprintf(&sbQuery, ` ORDER BY "%s" ASC`, q.PrimaryKey)
+
+	queryString := sbQuery.String()
+
+	var queryArgs []any
+
+	if q.LowerLimit.IsValid {
+		queryArgs = append(queryArgs, q.LowerLimit.Value)
+	}
+
+	if q.UpperLimit.IsValid {
+		queryArgs = append(queryArgs, q.UpperLimit.Value)
+	}
+
+	return pw.Query(ctx, queryString, queryArgs...)
+}

internal/app/db-wrapper/types.go

@@ -3,6 +3,8 @@ package dbwrapper
 import (
 	"context"
 	"errors"
+
+	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/models"
 )
 
 var MethodNotSupported error = errors.New("Method not supported by driver... yet :P")
@@ -24,6 +26,21 @@ type RowResult interface {
 	Scan(dest ...any) error
 }
 
+type ExtractorQueryLimit struct {
+	IsValid     bool
+	IsInclusive bool
+	Value       int64
+}
+
+type ExtractionQuery struct {
+	Schema     string
+	Table      string
+	PrimaryKey string
+	columns    []models.ColumnType
+	LowerLimit ExtractorQueryLimit
+	UpperLimit ExtractorQueryLimit
+}
+
 type DbWrapper interface {
 	Close() error
 	Connect(ctx context.Context, dbUrl string) error
@@ -32,4 +49,5 @@ type DbWrapper interface {
 	Query(ctx context.Context, query string, args ...any) (RowsResult, error)
 	QueryRow(ctx context.Context, query string, args ...any) RowResult
 	SaveMassive(ctx context.Context, schema string, table string, columnNames []string, rows [][]any) (int64, error)
+	QueryFromObject(ctx context.Context, query ExtractionQuery) (RowsResult, error)
 }