分组游标

• 对分组进行截取,处理分页和排序
• 本组件是对ShadowSql.Core同名组件的泛型扩展
• 支持对数据表类型特殊处理,增强功能、增加易用性

1. 接口

• ICursor

2. 基类

• CursorBase

3. 类

• GroupByTableCursor<TTable>

class GroupByTableCursor<TTable>
    where TTable : ITable;

4. ToCursor

4.1 ToCursor扩展方法

• 从sql分组创建分组游标

GroupByTableCursor<TTable> ToCursor<TTable>(this GroupByTableSqlQuery<TTable> groupBy, int limit = 0, int offset = 0)
        where TTable : ITable;

var cursor = _db.From("Employees")
    .SqlGroupBy("DepartmentId")
    .ToCursor();
    .CountAsc();
// SELECT * FROM [Employees] GROUP BY [DepartmentId] ORDER BY COUNT(*)

4.2 ToCursor重载扩展方法

• 从逻辑分组创建分组游标

GroupByTableCursor<TTable> ToCursor<TTable>(this GroupByTableQuery<TTable> groupBy, int limit = 0, int offset = 0)
        where TTable : ITable;

var cursor = _db.From("Employees")
    .GroupBy("DepartmentId")
    .ToCursor()
    .AggregateDesc(g => g.Max("Age"));
// SELECT * FROM [Employees] GROUP BY [DepartmentId] ORDER BY MAX([Age]) DESC

5. Take

• Take方法是ToCursor的平替

5.1 Take扩展方法

• 从sql分组创建分组游标

GroupByTableCursor<TTable> Take<TTable>(this GroupByTableSqlQuery<TTable> groupBy, int limit, int offset = 0)
        where TTable : ITable;

var cursor = _db.From("Employees")
    .SqlGroupBy("DepartmentId")
    .Take(10);
    .CountAsc();
// SELECT TOP 10 * FROM [Employees] GROUP BY [DepartmentId] ORDER BY COUNT(*)

5.2 Take重载扩展方法

• 从逻辑分组创建分组游标

GroupByTableCursor<TTable> Take<TTable>(this GroupByTableQuery<TTable> groupBy, int limit = 0, int offset = 0)
        where TTable : ITable;

var cursor = _db.From("Employees")
    .GroupBy("DepartmentId")
    .Take(10)
    .AggregateDesc(g => g.Max("Age"));
// SELECT TOP 10 * FROM [Employees] GROUP BY [DepartmentId] ORDER BY MAX([Age]) DESC

6. AggregateAsc方法

• 聚合正序

GroupByTableCursor<TTable> AggregateAsc(Func<TTable, IAggregateField> aggregate);

var cursor = new CommentTable()
    .SqlGroupBy(c => [c.PostId])
    .ToCursor()
    .AggregateAsc(c => c.Pick.Sum());
// SELECT * FROM [Comments] GROUP BY [PostId] ORDER BY SUM([Pick])

7. AggregateDesc方法

• 聚合正序

GroupByTableCursor<TTable> AggregateDesc(Func<TTable, IAggregateField> aggregate);

var cursor = new CommentTable()
    .GroupBy(c => [c.PostId])
    .ToCursor()
    .AggregateDesc(c => c.Pick.Sum());
// SELECT * FROM [Comments] GROUP BY [PostId] ORDER BY SUM([Pick]) DESC

8. 其他相关功能

• 本组件并非只有以上功能,其他功能参看以下文档:
• 参看GroupByTableCursor<TTable>的方法和扩展方法部分
• 参看游标简介
• 参看ShadowSqlCore相关文档