Question

我有以下情况：

我需要在EF上下文中执行以下linq查询

from table1 in context.TableOne
join table2 in context.TableTwo on table1.SomeFKId equals table2.Id
join table3 in context.TableThree on table2.SomeFKId equals table3.Id
...
join tableN in context.TableN on tableN_1.SomeFKId equals tableN.Id
where case1 && case2 && case3 ... && caseN
select new TablesDto { VarOne = table1.Var , VarTwo = tableN_2.var }

我的问题是我想在diffirent senarios中使用相同的查询，并且有很多扩展。我宁愿不写多次（DRY原则）只是扩展它，但不是以效率和速度为代价。

如果我想要将第一个表连接到另一个表，我可以扩展Dto以合并其余的变量但是如果我要遍历行，我需要每行查询来扩展它。由于我在谈论100到5000行，即使迭代也需要一些时间。

扩展包括：其他情况（case1，case2等）和其他连接。

扩展示例：

from table1 in context.TableOne
join table2 in context.TableTwo on table1.SomeFKId equals table2.Id
join table3 in context.TableThree on table2.SomeFKId equals table3.Id
...
join tableN in context.TableN on tableN_1.SomeFKId equals tableN.Id
join extTable in context.TableExt on table2.SomeFKId equals extTable.Id
where case1 && case2 && case3 ... && caseN || extTable.NumOfSmth == 4
select new ExtTablesDto { VarOne = table1.Var , VarTwo = tableN_2.var , ExtVar = extTable.Name }

Answer 1

试试这个......

void Main()
{
    using(var dal = new DataAccessLayer())
    {
        var items = dal.TablesDtoQuery.Case1().Case2().ToList();
    }
}

public class DataAccessLayer : IDisposable
{
    private DbContext context;

    public void Dispose()
    {
        context.Dispose();
    }

    public IQueryable<TablesDto> TablesDtoQuery
    {
        get
        {
            return 
                from table1 in context.TableOne
                join table2 in context.TableTwo on table1.SomeFKId equals table2.Id
                join table3 in context.TableThree on table2.SomeFKId equals table3.Id
                ...
                join tableN in context.TableN on tableN_1.SomeFKId equals tableN.Id
                where case1 && case2 && case3 ... && caseN
                select new TablesDto { VarOne = table1.Var , VarTwo = tableN_2.var };
        }
    }
}

public static class TablesDtoQueryExtension
{
    public IQueryable<TablesDto> Case1(this IQueryable<TablesDto> query)
    {
        return from t in query
            where ...
            select t;
    }

    public IQueryable<TablesDto> Case2(this IQueryable<TablesDto> query)
    {
        return from t in query
            where ...
            select t;
    } 
}

Answer 2

你可以像这样扩展where查询

var query = from user in dbContext.Users where user.id = 10;

if (x == 3)
{
   query = query.where(p=>p.name == "test");
}

等等你可以在这里扩展基本查询，你将在UserId = 10和name =＆＃34之后搜索;测试＆＃34;

如果您有EF模型，那么您应该尝试在那里创建表之间的依赖关系，然后您不需要在查询中加入它们

每个案例的EF扩展查询

2 个答案: