I'm trying to implement a query in LINQ that uses a left outer join with multiple conditions in the ON clause.
I'll use the example of the following two tables Project (ProjectID, ProjectName) and Task (TaskID, ProjectID, TaskName, Completed). I want to see the full list of all projects with their respective tasks, but only those tasks that are completed.
I cannot use a filter for Completed == true because that will filter out any projects that do not have completed tasks. Instead I want to add Completed == true to the ON clause of the join so that the full list of projects will be shown, but only completed tasks will be shown. Projects with no completed tasks will show a single row with a null value for Task.
Here's the foundation of the query.
from t1 in Projects
join t2 in Tasks
on new { t1.ProjectID} equals new { t2.ProjectID } into j1
from j2 in j1.DefaultIfEmpty()
select new { t1.ProjectName, t2.TaskName }
How do I add && t2.Completed == true to the on clause?
I can't seem to find any LINQ documentation on how to do this.
You just need to name the anonymous property the same on both sides
on new { t1.ProjectID, SecondProperty = true } equals
new { t2.ProjectID, SecondProperty = t2.Completed } into j1
Based on the comments of @svick, here is another implementation that might make more sense:
from t1 in Projects
from t2 in Tasks.Where(x => t1.ProjectID == x.ProjectID && x.Completed == true)
.DefaultIfEmpty()
select new { t1.ProjectName, t2.TaskName }
Here you go with:
from b in _dbContext.Burden
join bl in _dbContext.BurdenLookups on
new { Organization_Type = b.Organization_Type_ID, Cost_Type = b.Cost_Type_ID } equals
new { Organization_Type = bl.Organization_Type_ID, Cost_Type = bl.Cost_Type_ID }
You can't do it like that. The join clause (and the Join() extension method) supports only equijoins. That's also the reason, why it uses equals and not ==. And even if you could do something like that, it wouldn't work, because join is an inner join, not outer join.
Follow WeChat
Success story sharing
Want to stay one step ahead of the latest teleworks?
Subscribe Now相似问题
- What is the difference between "INNER JOIN" and "OUTER JOIN"?
- Multiple "order by" in LINQ
- SQL JOIN - WHERE clause vs. ON clause
- How to do joins in LINQ on multiple fields in single join
- Difference between JOIN and INNER JOIN
- INNER JOIN ON vs WHERE clause
- Join/Where with LINQ and Lambda
- LEFT OUTER JOIN in LINQ
- Group by in LINQ
and, not one equality of some “weird” object. And to prove my point, your code is wrong. For it work, you would have to havetrueon the left side andt2.Completeon the right.AND SecondProperty IN (123, 456). I'll be moving on to that challenge and any help you could give would be greatly appreciated.