Question

费用通过QuestionID和AnswerID外键链接到PropertySurvey中的AnsweredQuestion。成本也可以通过UnitsQuestionID链接到同一PropertySurvey中的AnsweredQuestion，并再次通过ReplacementQuestionID链接。以下是作为内部联接的查询 - 以避免@CraigStuntz regards as "messy"

的连接语法的方式编写

var propertyCosts = from aq in answeredQuestions
    from a in aq.Answers
    from c in costs
    where aq.QuestionID == c.QuestionID && a.ID == c.AnswerID
    from uq in answeredQuestions
    where uq.QuestionID == c.UnitsQuestionID 
                        && uq.PropertySurveyID == aq.PropertySurveyID
    from rq in answeredQuestions
    where rq.QuestionID == c.ReplacementQuestionID 
                        && rq.PropertySurveyID == aq.PropertySurveyID
    select new PropertyCost(aq.Question.Text, 
    a.Text, 
    c.Amount, 
    uq.IntegerAnswer.GetValueOrDefault(1), 
    rq.IntegerAnswer.GetValueOrDefault(0));

是否可以在没有DefaultIfEmpty内容的情况下使用左连接将其重写为UnitQuestion和ReplacementQuestion？

Answer 1

为了跟随Craig Stuntz，您需要拥有您的逻辑可以遵循的关联。

因此，为了模拟你的许多人，你会得到一个中间表，它与问题和答案之间有1-Many关联。您可以在此处使用“成本”，并且无需任何费用即可实现零成本。

所以

问题（QuestionId）1 - ＆gt; 1 .. *费用（QuestionId）答案（AnswerId）1 - ＆gt; 1 .. *费用（AnswerId）问题（QuestionId）1 - ＆gt; 0 .. *成本（UnitQuestionId）问题（QuestionId）1 - ＆gt; 0 .. *费用（ReplacementQuestionId）

然后在你的模型中创建关联

Question (Property = Costs) -- (Property = Question) Costs
Question (no mapping) -- (Property = UnitQuestion) Costs
Question (no mapping) -- (Property = ReplacementQuestion) Costs
Answer (Property = Costs) -- (Property = Answer) Costs

此查询应与查询的行为相匹配。

from aq in answeredQuestions
from c in aq.Costs
select new PropertyCost(aq.Question.Text, 
                        c.Answer.Text, 
                        c.Amount, 
                        c.UnitQuestion == null ? 0 : c.UnitQuestion.IntegerAnswer
                        c.ReplacementQuestion == null ? 0 : c.ReplacementQuestion.IntegerAnswer

Answer 2

//Make this problem less complicated to explain by abstracting the inner join 
//that we always need.
//For efficiency this should probably be put back in line
var A = from aq in answeredQuestions
        from a in aq.Answers
        from c in costs
        where aq.QuestionID == c.QuestionID && a.ID == c.AnswerID
        select new
        {
            QuestionText = aq.Question.Text,
            AnswerText = a.Text,
            Amount = c.Amount,
            PropertySurveyID = aq.PropertySurveyID,
            PropertySurvey = aq.PropertySurvey,
            UnitsQuestionID = c.UnitsQuestionID,
            UnitsQuestion = c.UnitsQuestion
        };


//This is how to do it using the explicit join keyword
var B = from a in A
        join lj in answeredQuestions on
            new { 
                   a.PropertySurveyID, 
                   UnitsQuestionID = a.UnitsQuestionID.GetValueOrDefault(0) 
                }
            equals new { 
                          lj.PropertySurveyID, 
                          UnitsQuestionID = lj.QuestionID 
                       }
            into unitQuestions
        from uq in unitQuestions.DefaultIfEmpty()
        select new PropertyCost(a.QuestionText,
                    a.AnswerText,
                    a.Amount,
                    uq == null ? 1 : uq.IntegerAnswer.GetValueOrDefault(1));

//I thought this might do it but the filter on the navigational property 
//means it's equivalent to an inner join
var C = from a in A
        from uq in a.PropertySurvey
                    .AnsweredQuestions
                    .Where(x => x.QuestionID == a.UnitsQuestionID)
        select new PropertyCost(a.QuestionText,
                    a.AnswerText,
                    a.Amount,
                    uq == null ? 1 : uq.IntegerAnswer.GetValueOrDefault(1));

//This is the solution
//Back to the basics described by @CraigStuntz
//Just that we have to navigate further to get to the Units value
//Is this less "messy" than a join? Not sure. Maybe if you can think in Linq...
var D = from a in A
        select new PropertyCost
        (
            a.QuestionText,
            a.AnswerText,
            a.Amount,
            a.PropertySurvey
                .AnsweredQuestions
                .Where(x => x.QuestionID == a.UnitsQuestionID)
                .FirstOrDefault() == null
            ?
            1
            : a.PropertySurvey
                .AnsweredQuestions
                .Where(x => x.QuestionID == a.UnitsQuestionID)
                .FirstOrDefault()
                .IntegerAnswer.GetValueOrDefault(1)
        );

//And here I have further refined it by putting the initial inner join back 
//inline and using the let keyword define how to retrieve the unit question. 
//This makes it much more readable:

var E = from aq in answeredQuestions
        from a in aq.Answers
        from c in costs
        let unitquestion = aq.PropertySurvey
            .AnsweredQuestions
            .Where(x => x.QuestionID == c.UnitsQuestionID)
            .FirstOrDefault()
        where aq.QuestionID == c.QuestionID && a.ID == c.AnswerID
        select new 
        {
            QuestionText = aq.Question.Text,
            AnswerText = a.Text,
            UnitCost = c.Amount,
            NumUnits = unitquestion == null ? 1 : unitquestion.IntegerAnswer ?? 1,
        };

花了我很长时间才得到这个。我仍然认为在sql中我不禁会被Use Views in Entity Framework诱惑。请注意我已将其简化为仅显示第一个左侧连接到UnitQuestion

使用Linq进行左连接而没有“混乱”连接

2 个答案: