convert ms sql sub query in select clause to linq2db C#

Question

Can some one help me in converting below ms sql query to linq2db c# query? I could not find any reference in linq2db documentation.

Any help or url to an example is highly appreciated.

SELECT
p.Id as ProductId,
(SELECT STRING_AGG(sao.Name, ',')
  FROM [Product_SpecificationAttribute_Mapping] PS
    JOIN [SpecificationAttributeOption] sao on sao.id=ps.SpecificationAttributeOptionId
    JOIN [SpecificationAttribute] sa on sa.id=sao.SpecificationAttributeId
    WHERE sa.Id=7 and ps.ProductId=p.Id) AS 'PrimaryTechnology',
(SELECT STRING_AGG(sao.Name, ',')
                                FROM [Product_SpecificationAttribute_Mapping] PS
    JOIN [SpecificationAttributeOption] sao on sao.id=ps.SpecificationAttributeOptionId
    JOIN [SpecificationAttribute] sa on sa.id=sao.SpecificationAttributeId
    WHERE sa.Id=8 and ps.ProductId=p.Id) AS 'SecondaryTechnology',
(SELECT sao.Name
    FROM [Product_SpecificationAttribute_Mapping] PS
    JOIN [SpecificationAttributeOption] sao on sao.id=ps.SpecificationAttributeOptionId
    JOIN [SpecificationAttribute] sa on sa.id=sao.SpecificationAttributeId
    WHERE sa.Id=1 and ps.ProductId=p.Id) AS 'ProfileType'
FROM [Product] p
order by P.Id asc