Linq2DB EF Core 循环连接表

Question

我正在使用linq2db.EntityFrameworkCore

我需要动态加入 DocumentMetadataValue 表加入 Document 表。

左连接表可以是 DocumentMetadataValue_1、DocumentMetadataValue_5、DocumentMetadataValue_9、DocumentMetadataValue_11 等。

如何使用 Linq2Db 实现这一点。

请在下面找到代码。这只是为了说明问题。所以它不起作用，因为它是问题。

var query2 = from p in dbContext.Document

foreach (JObject childRule in queryRule.rules)
{

    ChildRule rule = childRule.ToObject<ChildRule>();
    string DocumentFieldTable = string.Format("DocumentField_{0}", rule.id);

    //Here I need left join to query2.
    from op in projectContext.Set<DocumentMetadataValue>().ToLinqToDBTable().TableName(DocumentFieldTable).LeftJoin(op => op.DocumentId == p.Id);        
}
 //After above selection I will apply where clause here and will select p from query2.
 select p;

Answer 1

如果我明白你想要什么，你需要编写类似的东西（纯 linq2db，所以不要忘记添加 ToLinqToDBTable 调用）：

// define typed projection to include all possible joined tables
// otherwise you will need to write complex logic to build expressions
class Projection
{
    public Document doc { get; set; }
    public DocumentField field1 { get; set; }
    public DocumentField field2 { get; set; }
    public DocumentField field3 { get; set; }
}

// initial query typed as IQueryable<Projection>
var query = db.GetTable<Document>().Select(d => new Projection() { doc = d });
// select required joins (replace it with your query rules logic)
var with1 = true;
var with2 = false;
var with3 = true;

// add requested joins, note how we copy records
// from previous query to new projection
if (with1)
    query = query.LeftJoin(
        db.GetTable<DocumentField>().TableName("field_1"),
        (d, f) => d.doc.Id == f.DocumentId,
        (d, f) => new Projection () { doc = d.doc, field1 = f });
if (with2)
    query = query.LeftJoin(
        db.GetTable<DocumentField>().TableName("field_2"),
        (d, f) => d.doc.Id == f.DocumentId,
        (d, f) => new Projection() { doc = d.doc, field1 = d.field1, field2 = f });
if (with3)
    query = query.LeftJoin(
        db.GetTable<DocumentField>().TableName("field_3"),
        (d, f) => d.doc.Id == f.DocumentId,
        (d, f) => new Projection() { doc = d.doc, field1 = d.field1, field2 = d.field2, field3 = f });

// add filters
if (with1)
    query = query.Where(r => r.field1.FilterMe == "test1");
if (with2)
    query = query.Where(r => r.field2.FilterMe == "test2");
if (with3)
    query = query.Where(r => r.field3.FilterMe == "test3");

// select only documents
query.Select(r => r.doc).ToArray();

结果：

SELECT
    [d].[Id]
FROM
    [Document] [d]
        LEFT JOIN [field_1] [f_1] ON [d].[Id] = [f_1].[DocumentId]
        LEFT JOIN [field_3] [f_2] ON [d].[Id] = [f_2].[DocumentId]
WHERE
    [f_1].[FilterMe] = N'test1' AND [f_2].[FilterMe] = N'test3'

Answer 2

我相信你确实需要Inner join，下面你可以使用

/* DocumentMetadataValue_1, DocumentMetadataValue_5, DocumentMetadataValue_9, DocumentMetadataValue_11 */

var query2 = (from doc1 in dbContext.Document.DocumentMetadataValue_1 
join doc5 in dbContext.Document.DocumentMetadataValue_5
on doc1.id equals doc5.id
join doc9 in dbContext.Document.DocumentMetadataValue_9
on doc5.id equals doc9.id
join doc11 in dbContext.Document.DocumentMetadataValue_11
on doc5.id equals doc11.id).ToList();