使用LINQ创建具有1：N关系的实体的查询

Question

I know it's not something unusual to make such kind of queries but I think I get lost so I seek help. I have to tables with relation 1:N and to make it more clear I'll post a print screen from the management studio :

I am working on a asp.net mvc 3 project and I need to make a view where all Documents will be shown (and some filter and stuff, but I think that is irrelevant for this case). I need the data from the table Documents and only one specific record for each document from the DocumentFields table. This record is the record holding the name of the Document and it's uniqueness is DocumentID == Docmuents.Id, DocumentFields.RowNo == 1 and DocumentsFields.ColumnNo == 2. This is unique record for every Document and I need to get the FieldValue from this record which actually holds the Name of the Document.

I am not very sure how to build my query (maybe using JOIN) and I also would like to make my view strongly typed passing a model of type Documents but I'm not sure if it's possible, but I think depending on the way the query is build will determine the type of the model for the view.

Answer 1

I believe what you want is something like this:

var results = 
    from d in dbContext.Documents
    join df in dbContext.DocumentFields 
    on new { d.Id, RowNo = 1, ColumnNo = 2 } equals 
       new { Id = df.DocumentId, df.RowNo, df.ColumnNo }
    select new 
    {
        Document = d,
        DocumentName = df.FieldValue
    };

Of course if you set up navigation properties, you can just do this:

var results = 
    from d in dbContext.Documents
    let df = d.DocumentFields.First(x => x.RowNo == 1 && x.ColumnNo == 2)
    select new 
    {
        Document = d,
        DocumentName = df.FieldValue
    };