Join 2 lists in share point using CAML query - sharepoint

Question

I just use Sharepoint for few days and I know this question have asked many times but I've tried all of them and none of them work.
These are my design
Document as a Document Library type have a Id
Id | DocumentName
---+-------------
1 | Document A
2 | Document B
Activities list, have a foreign key 'DocId' that reference to the Document Id
Id | DocId | Name
---+-------+-----------
1 | 1 | Activity A
2 | 1 | Activity B
3 | 1 | Activity C
4 | 2 | Activity D
The Problem is I need to get all the Activities that included the document name on the Document.
In SQL I can use Join query to get the additional information from another table. But I have try some Join statement in CAML query and none of them work.
Here is the result that I need to get.
Id | DocId | Name | DocumentName
---+-------+--------------------------
1 | 1 | Activity A | Document A
2 | 1 | Activity B | Document A
3 | 1 | Activity C | Document A
4 | 2 | Activity D | Document B
Could any one please suggest me the query?
Here is my query:
<View>
<ViewFields>
<FieldRef Name = 'DocLeafRef'/>
<FieldRef Name = 'ID'/>
<FieldRef Name = 'e8_document'/>
<FieldRef Name = 'Title'/>
<FieldRef Name = 'Author'/>
<FieldRef Name = 'Created'/>
</ViewFields>
<Joins>
<Join Type = 'INNER' ListAlias = 'Documents'>
<Eq>
<FieldRef Name ='e8_document' RefType = 'Id'/>
<FieldRef Name ='ID' List ='Documents'/>
</Eq>
</Join>
</Joins>
<ProjectedFields>
<Field ShowField ='FileLeafRef' Type ='Lookup' Name ='DocLeafRef' List ='Documents'/>
</ProjectedFields>
<Query>
<Where>
<Eq>
<FieldRef Name='e8_caseId'></FieldRef>
<Value Type = 'Number'>23</Value>
</Eq>
</Where>
</Query>
</View>
I'm query on the Activities list and the e8_document is the lookup field that reference to the Id in the Document. As I understand we need the projection and I've added the projection but the query throws an error.

Answer 1

It seems the Query element is invalid in your case, basically Query element could not contain Joins as a child element.
Server-Side Object Model
For SPQuery Class Joins element needs to be specified via SPQuery.Joins Property:
var qry = new SPQuery();
qry.Joins = #"<Join Type="LEFT" ListAlias="Documents">
<Eq>
<FieldRef Name="DocId" RefType="ID" />
<FieldRef Name="ID" List="Documents" />
</Eq>
</Join>";
Client-Side Object Model
Here is the complete CAML query for CSOM API:
<View>
<ViewFields>
<FieldRef Name="ID" />
<FieldRef Name="DocId" />
<FieldRef Name="Name" />
<FieldRef Name="Documents" />
</ViewFields>
<Joins>
<Join Type="LEFT" ListAlias="Documents">
<Eq>
<FieldRef Name="DocId" RefType="ID" />
<FieldRef Name="ID" List="Documents" />
</Eq>
</Join>
</Joins>
<ProjectedFields>
<Field ShowField="DocumentName" Type="Lookup" Name="Documents" List="Documents" />
</ProjectedFields>
<Query />
</View>