dialect/sql: add option for adding and getting error from builders

dialect/sql/builder.go

@@ -1101,7 +1101,8 @@ func (p *Predicate) EqualFold(col, sub string) *Predicate {
 	return p.Append(func(b *Builder) {
 		f := &Func{}
 		f.SetDialect(b.dialect)
-		b.Ident(f.Lower(col))
+		f.Lower(col)
+		b.WriteString(f.String())
 		b.WriteOp(OpEQ)
 		b.Arg(strings.ToLower(sub))
 	})
@@ -1131,7 +1132,8 @@ func (p *Predicate) ContainsFold(col, sub string) *Predicate {
 		case dialect.Postgres:
 			b.Ident(col).WriteString(" ILIKE ")
 		default: // SQLite.
-			b.Ident(f.Lower(col)).WriteString(" LIKE ")
+			f.Lower(col)
+			b.WriteString(f.String()).WriteString(" LIKE ")
 		}
 		b.Arg("%" + strings.ToLower(sub) + "%")
 	})
@@ -1221,66 +1223,107 @@ func (p *Predicate) mayWrap(preds []*Predicate, b *Builder, op string) {
 // Func represents an SQL function.
 type Func struct {
 	Builder
+	fns []func(*Builder)
 }
 
 // Lower wraps the given column with the LOWER function.
 //
 //	P().EQ(sql.Lower("name"), "a8m")
 //
-func Lower(name string) string { return Func{}.Lower(name) }
+func Lower(ident string) string {
+	f := &Func{}
+	f.Lower(ident)
+	return f.String()
+}
 
 // Lower wraps the given ident with the LOWER function.
-func (f Func) Lower(name string) string {
-	return f.byName("LOWER", name)
+func (f *Func) Lower(ident string) {
+	f.byName("LOWER", ident)
 }
 
 // Count wraps the ident with the COUNT aggregation function.
-func Count(name string) string { return Func{}.Count(name) }
+func Count(ident string) string {
+	f := &Func{}
+	f.Count(ident)
+	return f.String()
+}
 
 // Count wraps the ident with the COUNT aggregation function.
-func (f Func) Count(ident string) string {
-	return f.byName("COUNT", ident)
+func (f *Func) Count(ident string) {
+	f.byName("COUNT", ident)
 }
 
 // Max wraps the ident with the MAX aggregation function.
-func Max(name string) string { return Func{}.Max(name) }
+func Max(ident string) string {
+	f := &Func{}
+	f.Max(ident)
+	return f.String()
+}
 
 // Max wraps the ident with the MAX aggregation function.
-func (f Func) Max(ident string) string {
-	return f.byName("MAX", ident)
+func (f *Func) Max(ident string) {
+	f.byName("MAX", ident)
 }
 
 // Min wraps the ident with the MIN aggregation function.
-func Min(name string) string { return Func{}.Min(name) }
+func Min(ident string) string {
+	f := &Func{}
+	f.Min(ident)
+	return f.String()
+}
 
 // Min wraps the ident with the MIN aggregation function.
-func (f Func) Min(ident string) string {
-	return f.byName("MIN", ident)
+func (f *Func) Min(ident string) {
+	f.byName("MIN", ident)
 }
 
 // Sum wraps the ident with the SUM aggregation function.
-func Sum(name string) string { return Func{}.Sum(name) }
+func Sum(ident string) string {
+	f := &Func{}
+	f.Sum(ident)
+	return f.String()
+}
 
 // Sum wraps the ident with the SUM aggregation function.
-func (f Func) Sum(ident string) string {
-	return f.byName("SUM", ident)
+func (f *Func) Sum(ident string) {
+	f.byName("SUM", ident)
 }
 
 // Avg wraps the ident with the AVG aggregation function.
-func Avg(name string) string { return Func{}.Avg(name) }
+func Avg(ident string) string {
+	f := &Func{}
+	f.Avg(ident)
+	return f.String()
+}
 
 // Avg wraps the ident with the AVG aggregation function.
-func (f Func) Avg(ident string) string {
-	return f.byName("AVG", ident)
+func (f *Func) Avg(ident string) {
+	f.byName("AVG", ident)
 }
 
 // byName wraps an identifier with a function name.
-func (f Func) byName(fn, ident string) string {
-	f.WriteString(fn)
-	f.Nested(func(b *Builder) {
-		b.Ident(ident)
+func (f *Func) byName(fn, ident string) {
+	f.Append(func(b *Builder) {
+		f.WriteString(fn)
+		f.Nested(func(b *Builder) {
+			b.Ident(ident)
+		})
 	})
-	return f.String()
+}
+
+// Append appends a new function to the function callbacks.
+// The callback list are executed on call to String.
+func (f *Func) Append(fn func(*Builder)) *Func {
+	f.fns = append(f.fns, fn)
+	return f
+}
+
+// String implements the fmt.Stringer.
+func (f *Func) String() string {
+	for _, fn := range f.fns {
+		fn(&f.Builder)
+	}
+	return f.Builder.String()
 }
 
 // As suffixed the given column with an alias (`a` AS `b`).
@@ -1833,6 +1876,7 @@ type Builder struct {
 	dialect      string        // configured dialect.
 	args         []interface{} // query parameters.
 	total        int           // total number of parameters in query tree.
+	errs         []error       // errors that added during the query construction.
 }
 
 // Quote quotes the given identifier with the characters based
@@ -1893,6 +1937,28 @@ func (b *Builder) WriteString(s string) *Builder {
 	return b
 }
 
+// AddError appends an error to the builder errors.
+func (b *Builder) AddError(err error) *Builder {
+	b.errs = append(b.errs, err)
+	return b
+}
+
+// Err returns a concatenated error of all errors encountered during
+// the query-building, or were added manually by calling AddError.
+func (b *Builder) Err() error {
+	if len(b.errs) == 0 {
+		return nil
+	}
+	br := strings.Builder{}
+	for i := range b.errs {
+		if i > 0 {
+			br.WriteString("; ")
+		}
+		br.WriteString(b.errs[i].Error())
+	}
+	return fmt.Errorf(br.String())
+}
+
 // An Op represents a predicate operator.
 type Op int
 

dialect/sql/builder_test.go

@@ -5,6 +5,7 @@
 package sql
 
 import (
+	"fmt"
 	"strconv"
 	"strings"
 	"testing"
@@ -1242,3 +1243,12 @@ WHERE
 		})
 	}
 }
+
+func TestBuilder_Err(t *testing.T) {
+	b := Select("i-")
+	require.NoError(t, b.Err())
+	b.AddError(fmt.Errorf("invalid"))
+	require.EqualError(t, b.Err(), "invalid")
+	b.AddError(fmt.Errorf("unexpected"))
+	require.EqualError(t, b.Err(), "invalid; unexpected")
+}