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本文主要研究一下gorm的DeletedAt

DeletedAt

gorm.io/gorm@v1.20.10/soft_delete.go

type DeletedAt sql.NullTime

// Scan implements the Scanner interface.
func (n *DeletedAt) Scan(value interface{}) error {
    return (*sql.NullTime)(n).Scan(value)
}

// Value implements the driver Valuer interface.
func (n DeletedAt) Value() (driver.Value, error) {
    if !n.Valid {
        return nil, nil
    }
    return n.Time, nil
}

func (n DeletedAt) MarshalJSON() ([]byte, error) {
    if n.Valid {
        return json.Marshal(n.Time)
    }
    return json.Marshal(nil)
}

func (n *DeletedAt) UnmarshalJSON(b []byte) error {
    if string(b) == "null" {
        n.Valid = false
        return nil
    }
    err := json.Unmarshal(b, &n.Time)
    if err == nil {
        n.Valid = true
    }
    return err
}

func (DeletedAt) QueryClauses(f *schema.Field) []clause.Interface {
    return []clause.Interface{SoftDeleteQueryClause{Field: f}}
}

func (DeletedAt) DeleteClauses(f *schema.Field) []clause.Interface {
    return []clause.Interface{SoftDeleteDeleteClause{Field: f}}
}

DeletedAt为sql.NullTime类型，它实现了Scanner接口的Scan方法，实现了Valuer接口的Value方法；同时定义了MarshalJSON、UnmarshalJSON方法，还定义了QueryClauses方法，使用的是SoftDeleteQueryClause；DeleteClauses方法使用的是SoftDeleteDeleteClause

SoftDeleteQueryClause

gorm.io/gorm@v1.20.10/soft_delete.go

type SoftDeleteQueryClause struct {
    Field *schema.Field
}

func (sd SoftDeleteQueryClause) Name() string {
    return ""
}

func (sd SoftDeleteQueryClause) Build(clause.Builder) {
}

func (sd SoftDeleteQueryClause) MergeClause(*clause.Clause) {
}

func (sd SoftDeleteQueryClause) ModifyStatement(stmt *Statement) {
    if _, ok := stmt.Clauses["soft_delete_enabled"]; !ok {
        if c, ok := stmt.Clauses["WHERE"]; ok {
            if where, ok := c.Expression.(clause.Where); ok && len(where.Exprs) > 1 {
                for _, expr := range where.Exprs {
                    if orCond, ok := expr.(clause.OrConditions); ok && len(orCond.Exprs) == 1 {
                        where.Exprs = []clause.Expression{clause.And(where.Exprs...)}
                        c.Expression = where
                        stmt.Clauses["WHERE"] = c
                        break
                    }
                }
            }
        }

        stmt.AddClause(clause.Where{Exprs: []clause.Expression{
            clause.Eq{Column: clause.Column{Table: clause.CurrentTable, Name: sd.Field.DBName}, Value: nil},
        }})
        stmt.Clauses["soft_delete_enabled"] = clause.Clause{}
    }
}

SoftDeleteQueryClause的ModifyStatement方法会追加DeletedAt为nil的查询条件

SoftDeleteDeleteClause

gorm.io/gorm@v1.20.10/soft_delete.go

type SoftDeleteDeleteClause struct {
    Field *schema.Field
}

func (sd SoftDeleteDeleteClause) Name() string {
    return ""
}

func (sd SoftDeleteDeleteClause) Build(clause.Builder) {
}

func (sd SoftDeleteDeleteClause) MergeClause(*clause.Clause) {
}

func (sd SoftDeleteDeleteClause) ModifyStatement(stmt *Statement) {
    if stmt.SQL.String() == "" {
        curTime := stmt.DB.NowFunc()
        stmt.AddClause(clause.Set{{Column: clause.Column{Name: sd.Field.DBName}, Value: curTime}})
        stmt.SetColumn(sd.Field.DBName, curTime, true)

        if stmt.Schema != nil {
            _, queryValues := schema.GetIdentityFieldValuesMap(stmt.ReflectValue, stmt.Schema.PrimaryFields)
            column, values := schema.ToQueryValues(stmt.Table, stmt.Schema.PrimaryFieldDBNames, queryValues)

            if len(values) > 0 {
                stmt.AddClause(clause.Where{Exprs: []clause.Expression{clause.IN{Column: column, Values: values}}})
            }

            if stmt.ReflectValue.CanAddr() && stmt.Dest != stmt.Model && stmt.Model != nil {
                _, queryValues = schema.GetIdentityFieldValuesMap(reflect.ValueOf(stmt.Model), stmt.Schema.PrimaryFields)
                column, values = schema.ToQueryValues(stmt.Table, stmt.Schema.PrimaryFieldDBNames, queryValues)

                if len(values) > 0 {
                    stmt.AddClause(clause.Where{Exprs: []clause.Expression{clause.IN{Column: column, Values: values}}})
                }
            }
        }

        if _, ok := stmt.Clauses["WHERE"]; !stmt.DB.AllowGlobalUpdate && !ok {
            stmt.DB.AddError(ErrMissingWhereClause)
        } else {
            SoftDeleteQueryClause{Field: sd.Field}.ModifyStatement(stmt)
        }

        stmt.AddClauseIfNotExists(clause.Update{})
        stmt.Build("UPDATE", "SET", "WHERE")
    }
}

SoftDeleteDeleteClause的ModifyStatement方法会设置DeletedAt为当前时间

interfaces

gorm.io/gorm@v1.20.10/schema/interfaces.go

type GormDataTypeInterface interface {
    GormDataType() string
}

type CreateClausesInterface interface {
    CreateClauses(*Field) []clause.Interface
}

type QueryClausesInterface interface {
    QueryClauses(*Field) []clause.Interface
}

type UpdateClausesInterface interface {
    UpdateClauses(*Field) []clause.Interface
}

type DeleteClausesInterface interface {
    DeleteClauses(*Field) []clause.Interface
}

interfaces包定义了QueryClausesInterface、DeleteClausesInterface接口；schema的Parse方法会回调这些interface的对应方法

小结

gorm的DeletedAt为sql.NullTime类型，它定义了QueryClauses方法，使用的是SoftDeleteQueryClause，它的ModifyStatement方法会追加DeletedAt为nil的查询条件；DeleteClauses方法使用的是SoftDeleteDeleteClause，它的ModifyStatement方法会设置DeletedAt为当前时间。

doc

• gorm