github.com/ecodeclub/eorm@v0.0.2-0.20231001112437-dae71da914d0/internal/merger/pagedmerger/merger.go (about)

     1  // Copyright 2021 ecodeclub
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  // http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package pagedmerger
    16  
    17  import (
    18  	"context"
    19  	"database/sql"
    20  	"sync"
    21  
    22  	"github.com/ecodeclub/eorm/internal/rows"
    23  
    24  	"github.com/ecodeclub/eorm/internal/merger"
    25  	"github.com/ecodeclub/eorm/internal/merger/internal/errs"
    26  )
    27  
    28  type Merger struct {
    29  	m      merger.Merger
    30  	limit  int
    31  	offset int
    32  }
    33  
    34  func NewMerger(m merger.Merger, offset int, limit int) (*Merger, error) {
    35  	if offset < 0 || limit <= 0 {
    36  		return nil, errs.ErrMergerInvalidLimitOrOffset
    37  	}
    38  
    39  	return &Merger{
    40  		m:      m,
    41  		limit:  limit,
    42  		offset: offset,
    43  	}, nil
    44  }
    45  
    46  func (m *Merger) Merge(ctx context.Context, results []rows.Rows) (rows.Rows, error) {
    47  	rs, err := m.m.Merge(ctx, results)
    48  	if err != nil {
    49  		return nil, err
    50  	}
    51  	err = m.nextOffset(ctx, rs)
    52  	if err != nil {
    53  		return nil, err
    54  	}
    55  	return &Rows{
    56  		rows:  rs,
    57  		mu:    &sync.RWMutex{},
    58  		limit: m.limit,
    59  	}, nil
    60  }
    61  
    62  // nextOffset 会把游标挪到 offset 所指定的位置。
    63  func (m *Merger) nextOffset(ctx context.Context, rows rows.Rows) error {
    64  	offset := m.offset
    65  	for i := 0; i < offset; i++ {
    66  		if ctx.Err() != nil {
    67  			return ctx.Err()
    68  		}
    69  		// 如果偏移量超过rows结果集返回的行数，不会报错。用户最终查到0行
    70  		if !rows.Next() {
    71  			return rows.Err()
    72  		}
    73  	}
    74  	return nil
    75  }
    76  
    77  type Rows struct {
    78  	rows    rows.Rows
    79  	limit   int
    80  	cnt     int
    81  	lastErr error
    82  	closed  bool
    83  	mu      *sync.RWMutex
    84  }
    85  
    86  func (*Rows) NextResultSet() bool {
    87  	return false
    88  }
    89  
    90  func (r *Rows) Next() bool {
    91  	r.mu.Lock()
    92  	if r.closed {
    93  		r.mu.Unlock()
    94  		return false
    95  	}
    96  	if r.cnt >= r.limit || r.lastErr != nil {
    97  		r.mu.Unlock()
    98  		_ = r.Close()
    99  		return false
   100  	}
   101  	canNext, err := r.nextVal()
   102  	if err != nil {
   103  		r.lastErr = err
   104  		r.mu.Unlock()
   105  		_ = r.Close()
   106  		return false
   107  	}
   108  	if !canNext {
   109  		r.mu.Unlock()
   110  		_ = r.Close()
   111  		return canNext
   112  	}
   113  	r.cnt++
   114  	r.mu.Unlock()
   115  	return canNext
   116  }
   117  func (r *Rows) nextVal() (bool, error) {
   118  	if r.rows.Next() {
   119  		return true, nil
   120  	}
   121  	if r.rows.Err() != nil {
   122  		return false, r.rows.Err()
   123  	}
   124  	return false, nil
   125  }
   126  
   127  func (r *Rows) Scan(dest ...any) error {
   128  	r.mu.RLock()
   129  	defer r.mu.RUnlock()
   130  	if r.lastErr != nil {
   131  		return r.lastErr
   132  	}
   133  	if r.closed {
   134  		return errs.ErrMergerRowsClosed
   135  	}
   136  	return r.rows.Scan(dest...)
   137  }
   138  
   139  func (r *Rows) Close() error {
   140  	r.mu.Lock()
   141  	defer r.mu.Unlock()
   142  	r.closed = true
   143  	return r.rows.Close()
   144  }
   145  
   146  func (r *Rows) ColumnTypes() ([]*sql.ColumnType, error) {
   147  	return r.rows.ColumnTypes()
   148  }
   149  func (r *Rows) Columns() ([]string, error) {
   150  	return r.rows.Columns()
   151  }
   152  
   153  func (r *Rows) Err() error {
   154  	r.mu.RLock()
   155  	defer r.mu.RUnlock()
   156  	return r.lastErr
   157  }