SAP HANA : CDS

6.SAP HANA CDS

使用SAP HANA Core Data Services（CDS）在SAP HANA Extended Application Services中构建设计时数据持久性模型。

CDS创建持久性Model类型：

tables (entities)

SQL views

associations between entities or views

user-defined structured types

SAP HANA Studio,选择Package,右键New->创建Database Development->DDL Source File;

DDL Source File可以选择创建多种模板；

默认创建空的Context;

代码实例1：

namespace:文件的package路径，package路径的大小写必须一致；

using:通过引用其他package路径下文件中定义的type,实现类型的共享;

@Schema:这个批注表示使用的Schema;

context:上下文，其中可以包含多种持久化结构定义；

//：表示单行注释；

/**/:表示多行注释；

namespace test.tom;
using test.tom::CDS_TEST_TYPE.test_type;
@Schema: 'TEST'
context CDS_TEST {
    //单行注释
    /*
    多行注释
    */
};

同样package路径test.tom下创建CDS_TEST_TYPE.hdbdd文件，

context CDS_TEST_TYPE {
    type test_type : Integer;
    type test_struct_type{
         test_type1 : String(20);
         test_type2 : String(30);
    };
};

代码实例2：

定义数据类型，可以在Context中定义单个类型，也可以多个类型集合

HANA数据类型和.hdbdd文件定义类型对应关系：

SAP HANA Type (hdbtable)	CDS Type (hdbdd)
NVARCHAR	String
SHORTTEXT	String
NCLOB	LargeString
TEXT	LargeString
VARBINARY	Binary
BLOB	LargeBinary
INTEGER	Integer
INT	Integer
BIGINT	Integer64
DECIMAL(p,s)	Decimal(p,s)
DECIMAL	DecimalFloat
DOUBLE	BinaryFloat
DAYDATE	LocalDate
DATE	LocalDate
SECONDTIME	LocalTime
TIME	LocalTime
SECONDDATE	UTCDateTime
LONGDATE	UTCTimestamp
TIMESTAMP	UTCTimestamp
ALPHANUM	hana.ALPHANUM
SMALLINT	hana.SMALLINT
TINYINT	hana.TINYINT
SMALLDECIMAL	hana.SMALLDECIMAL
REAL	hana.REAL
VARCHAR	hana.VARCHAR
CLOB	hana.CLOB
BINARY	hana.BINARY
ST_POINT	hana.ST_POINT
ST_GEOMETRY	hana.ST_GEOMETRY

    /*定义类型*/
    //单个类型
    type t1_char200 : String(200);
    //类型集
    type t1_collection{
    field1 : Integer;
    field2 : String(20);
    }

代码实例3：

嵌套Context, Context中定义类型可以使用；

    /*嵌套Context*/
    context MyContext1{
    //定义type
    type t2_char10 : String(10);
    //使用上层单个type
    type t2_sin_type : t1_char200;
    //使用上层类型集中type
    type t2_col_type : type of t1_collection.field2;
    }

代码实例4：

创建entity(table)类型

 /*定义entity(table)*/
 context MyContext2{
    //定义user table
    entity MyUser{
             key ID : Integer; //key设置为键值
             Name : String(100) not null; //不能为空
             Address : String(200) default 'CN'; //设置默认值
             Account : Decimal(15,2);
             Telephone : String(12);
         };
    //定义默认值测试table
    entity MyDefault{
         //generated [always | by default] as identity
         //Defining an element with IDENTITY is not supported in XS Classic
         //定义自增
         //key id : Integer generated always as identity(start with 1 increment by 1);
             field1 :  Integer       default -42;
             field2 :  Integer64     default 9223372036854775807;
             field3 :  Decimal(5,3)  default 12.345;
             field4 :  BinaryFloat   default 123.456e-1;
             field5 :  LocalDate     default date'2013-04-29';
             field6 :  LocalTime     default time'17:04:03';
             field7 :  UTCDateTime   default timestamp'2013-05-01 01:02:03';
             field8 :  UTCTimestamp  default timestamp'2013-05-01 01:02:03';
             //field9 :  Binary(32)    default x'0102030405060708090a0b0c0d0e0123[...]';
             field10 : String(10)    default 'foo';
         //generated always as <expression>
         //Generated calculated elements not supported in XS Classic
         //定义公式
         //field11 : Decimal(10,3) generated always as field1 + field3;
    };
    //定义table
    //通过批注等配置存储方式，index
    @Catalog:{
        tableType : #COLUMN,
             index : [
                  { name:'Index1', order:#DESC, unique:true,  elementNames:['ID'] },
                  { name:'Index2', order:#DESC, unique:false, elementNames:['name'] }
                    ]
         }
    entity Books{
         key ID : Integer;
         name : String(20);
         Editor: String(100);
    };

    //通过technical设置存储方式，index
    entity Author{
         key ID : Integer;
         name : String(20);
         Address : String(100);
    } technical configuration {
              row store;
              index MyIndex1 on (name) asc;
              unique index MyIndex2 on (ID,name) desc;
    };
}

代码实例5：

定义Table之间Associations,Table之间外键关系；

    //定义table
    //定义Annotation关系，类似于Table直接外键。
    context SimpleAssociations{
             type StreetAddress{
                 name : String(80);
                 number : Integer;
             };

             type CountryAddress{
                 name : String(80);
                 code : String(3);
             };

             entity Address{
                 key id : Integer;
                 street : StreetAddress;
                 zipCode : Integer;
                 city : String(80);
                 country : CountryAddress;
                 type : String(10); // home, office
             };

             entity Person{
                 key id : Integer;
                 // address1,2,3 are to-one associations
                 address1 : Association to Address;
                 address2 : Association to Address { id };
                 address3 : Association[1] to Address { zipCode, street, country };
                 // address4,5,6 are to-many associations
                 address4 : Association[0..*] to Address { zipCode };
                 address5 : Association[*] to Address { street.name };
                 address6 : Association[*] to Address { street.name AS streetName,country.name AS countryName };
                 //对订单关系
                 orders : Association[*] to SalesOrder on orders.Person_id = id;
             };

             //订单和人员，Item之间关系
             entity SalesOrder{
             key Order_id : Integer;
             key Item_id : Integer;
             key Person_id : Integer;
             count : Decimal(18,2);
             //对person,item关系,1個張訂單對應一個人，一個訂單對應多個訂單Item
             person : Association[1] to Person on person.id = Person_id;
             item : Association[*] to Item on item.id = Item_id;
             };

             //订单item
             entity Item{
             key id : Integer;
             name : String(20);
             //对应SalesOrder关系
             orders : Association[1] to SalesOrder on orders.Item_id = id;
             };
         }

代码实例6：

通过CDS,创建View;

View只能通过查询Table生成；

/*定义View*/
Context MyContext3{
    //const定义常量
    const number1 : Integer = 4;

    entity test{
         name : String(20);
         a : Integer;
         b : Integer;
    };
    entity test1{
         name : String(20);
         a : Decimal(10,2);
         b : Integer;
    }

    　　 //定义View,查询MyContext2.SimpleAssociations路径,括号中定义查询字段
        view AddressView as select from MyContext2.SimpleAssociations.Address{
             id,
             street.name,
             street.number
         };

         //表达式,计算+，-，*，/,||连接操作,case when操作
         view CalView as select from test{
             a + b AS data_sum,
             a - b AS data_sub,
             a * 1 AS data_mul,
             a / 1 AS data_div,
             -1 AS data_neg,
             a || b AS data_con,
             CASE WHEN a > 10 THEN 'large'
                  WHEN a > 20 THEN 'l large'
             ELSE 'none'
             END AS data_case
         };

         //统计function
         //AVG,COUNT,MIN,MAX,SUM,STDDEV,VAR
         //where条件
         //group by分组
         //having 统计function条件
         //order by 排序，
         //limit xx offset xx限制条数
         view FuncView as select from test{
             name,
             AVG(a) AS data_avg,
             COUNT(*) AS data_count,
             MIN(a) AS data_min,
             MAX(a) AS data_max,
             SUM(a) AS data_sum,
             STDDEV(a) AS data_stddev,
             VAR(a) AS data_var
         }where name in('tom','jim','tian')
         group by name  //分组
         having AVG(a) > 100
         order by name limit 1 offset 30
         ;

         //UNION操作
         view UnionView as select from test{name,a,b}
                            union
                            select from test1{name,a,b};
         //Join操作
         //[ INNER ] JOIN
         //LEFT [ OUTER ] JOIN
         //RIGHT [ OUTER ] JOIN
         //FULL [ OUTER ] JOIN
         //CROSS JOIN
         view JoinView as select from test join test1 on test.name = test1.name{
             test.name,
             test.a + test1.a as a,
             test.b + test1.b as b
         };

         //top 前几条记录，distinct去重
         view topView as select from test top 10 {
             name,
             a,
             b
         };

         view distinctView as select from test distinct{
             name
         };

         //定义具有参数的View
         //parameter names :只能由大写字母，数字，下划线组成，不能数字开头
         //Views with parameters are not supported in XS Classic
         /*
         view paramView with parameters PAR1 : Integer,
                                          PAR2 : String(20)
         as select from test{
             name,
             a,
             b + $parameters.PAR1 AS b
         }where name = $parameters.PAR2;
         */

         //查询该Schema下实体Table;
         //不能多个Schema Table 混合同时访问；
         //@Schema批注指定Schema
         view tableView as select from TEST_SFLIGHT distinct{
             CARRID,
             CONNID
         };
         /*
         view tableView1 as select from SFLIGHT distinct{
             CARRID,
             CONNID
         };
         */

}

参考資料：

https://help.sap.com/docs/SAP_HANA_PLATFORM/09b6623836854766b682356393c6c416/0b1eb07d74ec4f91947ff4cc4f557429.html?locale=en-US