如何从SQL Server中的EAV表创建JSON

Question

如果你有一个简单的表,如:

Id Name Age  
1  Saeed 32  
2  John  28  
3  David 34

然后,您可以For XML在SQL Server中使用以下命令创建JSON :

select '{ name : "' + Name + '", age : ' + age + ' }'
from People
where Id = 1
for xml path('')

这很容易,因为预先知道列.但是,我坚持从EAV表创建JSON.例如,如果表是:

Id EntityId Key    Value
1  1        Name   Saeed
2  1        Age    32
3  1        Gender Male
4  1        Key1   Value1
5  1        Key2   Value2

我该如何创建这个JSON？

{ Name: "Saeed", Age: 32, Gender: "Male", Key1: "Value1", Key2: "Value2" }

从这个查询:

select *
from PeopleEav
where EntityId = 1

请注意,键的数量是可变的(它是一个EAV表).

Answer 1

试试这个 -

DECLARE @PeopleEav TABLE
(
      Id INT IDENTITY(1,1)
    , EntityId INT
    , [Key] VARCHAR(30)
    , Value VARCHAR(100)
)

INSERT INTO @PeopleEav (EntityId, [Key], Value)
VALUES
    (1, 'Name',   'Saeed'),
    (1, 'Age',    '32'),
    (1, 'Gender', 'Male'),
    (1, 'Key1',   'Value1'),
    (1, 'Key2',   'Value2')

SELECT 
      t.EntityId
    , JSON = STUFF((
        SELECT ', ' + [Key] + ': "' + Value + '"'
        FROM @PeopleEav t2
        WHERE t2.EntityId = t2.EntityId
        FOR XML PATH(''), TYPE).value('.', 'NVARCHAR(MAX)'), 1, 2, '{ ') + ' }'                  
FROM (
    SELECT DISTINCT EntityId
    FROM @PeopleEav
) t
--WHERE EntityId = 1

输出 -

EntityId    JSON
----------- --------------------------------------------------------------------------------------------
1           { Name: "Saeed", Age: "32", Gender: "Male", Key1: "Value1", Key2: "Value2" }