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How to make linq lambda expression

select a.ObjectFieldID,
a.FieldName,
b.RelationName
from tblMNG_Framework_ObjectField as a left join
tblMNG_Framework_ObjectRelation as b on a.ObjectID = b.RelatedObjectID
and a.ObjectFieldID = b.RelatedKeyFieldID
where a.ObjectID = 2
and a.Deleted = 0

It's my quick code, I have no data to test so feedback me with your data sample if left join is not exact.
tblMNG_Framework_ObjectField.GroupJoin(tblMNG_Framework_ObjectRelation,
a => new { JoinCol1 = a.ObjectID, JoinCol2 = a.ObjectFieldID },
b => new { JoinCol1 = b.RelatedObjectID, JoinCol2 = b.RelatedKeyFieldID },
(a, b) => new { a, b }).Where(x => x.a.ObjectID == 2 && x.a.Deleted == 0)
.SelectMany(b => b.b.DefaultIfEmpty(),
(a, b) => new { a.a.ObjectID, a.a.FieldName, b.RelationName });
Hope it helps

joining two from with an expression<func<>>

Is it possible to join two from based on a local expression variable?
ex;
var query = from t in context.table1
from a in context.anothertable1.Where(x => t.id == a.id)
select new {a,t};
on line 2, the Where clause .Where(x => t.id == a.id) how would you move it into an expression?
I know i can do this;
Expression<Func<anothertable1, bool>> test = x => x.field1 == 1;
and It would work here;
var query = from t in context.table1
from a in context.anothertable1
.Where(x => t.id == a.id)
.Where(test)
select new {a,t};
and everything work and the sql query generated is as expected.
I can't figure out how to do the same with the other where.
EDIT
a more complex example, i anonymized it so it might not compile
var listOfMinMaxtable1 = (from n in context.table1.Where(table1Filter)
group n by n.table1_Number into grp
select new MinMaxtable1()
{
table1_Id_Max = grp.Max(x => x.table1_Id),
table1_Id_Min = grp.Min(x => x.table1_Id),
table1_Number = grp.Key
});
var listtable2 = (from t in context.table2
group t by t.table2_Id into grp
select new table2()
{
table2 = grp,
table2_Id = grp.Key
});
var query = from MinMax in listOfMinMaxtable1
//inner join **reference 1**
from table3 in context.table3
.Where(x => x.table_Number == MinMax.table_Number)
.Where(noticeMasterFilter) //a working expression<func<>>
//inner join **reference 2**
from Lasttable1 in context.table1
.Where(x => x.table_Id == MinMax.table_Id_Max)
//left join **reference 3**
from Firsttable1 in context.table1
.Where(x => x.table_Id == MinMax.table_Id_Min)
.Where(firstNoticeFilter) //a working expression<func<>>
.DefaultIfEmpty()
//left join **reference 4**
from Lasttable2 in listtable2
.Where(x => x.table_Id == MinMax.table_Id_Max)
.SelectMany(x => x.table2)
.Where(x => x.table2_Id == 123)
.OrderByDescending(x => x.table_Id)
.Take(1)
.DefaultIfEmpty()
if you find //left join reference 3 in the code above
that where clause; .Where(x => x.table_Id == MinMax.table_Id_Min)
might be sometime; .Where(x => x.table_Id == MinMax.table_Id_Max)
I could just copy/paste the whole from and change the where clause while adding noop pattern (an expression that return false and this make entity framework remove the whole thing so it doesn't affect the generated sql/result) with an expression on both from
for reference(this is noise to the question), the noop expression that i'm talking about is;
Expression<Func<table1, bool>> includeFrom= x => false;
and would be used like
//left join **reference 3**
from Firsttable1 in context.table1
.Where(x => x.table_Id == MinMax.table_Id_Min)
.Where(firstNoticeFilter) //a working expression<func<>>
.Where(includeFrom) //<--- this line make it a noop if the expression stay false
.DefaultIfEmpty()
but I don't want to do this if it's possible to make a custom expression that would go into the .Where()

Instead of creating an expression based on one type, you can create a combined type and use that for your where expression.
Two Table Combined Type
public class TwoTableDto
{
public Table1 t { get; set; }
public Table2 a { get; set; }
}
Query without expression
var query = (from t in context.table1
from a in context.anothertable1
select new TwoTableDto { t = t, a = a })
.Where(x => x.t.id == x.a.id);
Expression
Expression<Func<TwoTableDto, bool>> expr = x => x.t.id == x.a.id;
Query with expression
var query = (from t in context.table1
from a in context.anothertable1
select new TwoTableDto { t = t, a = a })
.Where(expr);

Converting query to lambda expression with joins and where clause

I have this query and I'm having trouble converting into a lambda expression
SELECT [dbo].[Prospects].[Id]
,[UserId]
,[NewId]
,[dbo].[Prospects].[Status]
FROM [dbo].[Prospects] join [dbo].[User] on [dbo].[User].Id = [dbo]. [Prospects].UserId
where [dbo].[Prospects].NewId = 3 and [dbo].[User].IsActive = 1
This is what i got, but it is not working
var result = Workspace.Prospects.Join
(Workspace.Users, pros => pros.UserId,
use => use.Id, (pros, use)
=> new { Prospect = pros, User = use}).Where
(both => both.User.IsActive == true && both.Prospect.NewId == idVacante)
.OrderBy(both => both.Prospect.Id).AsEnumerable().ToList();
List<Prospect> prospects = result.Cast<Prospect>().ToList();

It's not that hard. you can filter the tables before joining them
var result = Workspace.Prospects.Where(x=> x.NewId == 3)
.Join(Workspace.Users.Where(x => x.IsActive == 1),
p => p.UserId,
u => u.Id,
(p, u) => new { p.Id, p.UserId, p.NewId, p.Status })

SQL query to LINQ conversion with nested select statements

I want to convert the following query to LINQ:
SELECT LV.* FROM LowerVehicles LV
INNER JOIN (Select VSerial,MAX(updatedOn) MaxUpdatedOn from LowerVehicles group by vserial) LVG
ON LV.VSerial = LVG.VSerial AND LV.updatedOn = LVG.MaxUpdatedOn

Not knowing your entities classes, here is an approximation. You can use query syntax or fluent syntax. Sometimes one is preferable over the other, and in the case of joins and grouping I prefer to use query syntax.
QUERY SYNTAX
var query = from LV in LowerVehicles
join LVG in (
from r in LowerVehicles
group r by r.vserial into g
select new {VSerial = g.Key, MaxUpdatedOn = g.Max(t => t.updatedOn)})
on LV.VSerial equals LVG.Vserial
and LV.updatedOn equals LVG.MaxUpdatedOn
select LV;
FLUENT SYNTAX
var lvg = LowerVehicles.GroupBy(t => t.vserial)
.Select(g => new {
VSerial = g.Key,
MaxUpdatedOn = g.Max(t => t.updatedOn)
});
var query = LowerVehicles.Join(
lvg,
a => new { a.VSerial, a.updatedOn },
b => new { b.VSerial, b.MaxUpdatedOn },
(a, b) => new { LV = a, LVG = b}
)
.Select(t=> t.LV);

Something like this?
Something.LowerVehicles
.Join(something.LowerVehicles.Select(y => new { y.VSerial, updatedOn = y.updatedOn.Max() }).GroupBy(z => z.VSerial),
x => new { x.VSerial, x.updatedOn },
lvg => new { lvg.VSerial, lvg.updatedOn },
(x, y) => x)

Combining Tables without JOIN using Lambda Expression

Combining Tables without JOIN keyword
var res2 = from u in dtEmp.AsEnumerable()
from v in dtDept.AsEnumerable()
where u.Field<int>("DepartmentID") == v.Field<int>("DepartmentID") &&
u.Field<double>("Salary") > 10000
select new
{
Name = u.Field<string>("Name"),
Department = v.Field<string>("DepartmentName")
};
How to do the same using Lambda Expression without using Join Keyword?

Do you mean you want to switch from SQL syntax to Method Chain syntax? i.e:
var res2 = dtEmp.AsEnumerable()
.SelectMany(u => dtDept.AsEnumerable(), (u, v) => new {u, v})
.Where(#t => u.Field<int>("DepartmentID") == v.Field<int>("DepartmentID") &&
u.Field<double>("Salary") > 10000).Select(#t => new
{
Name = u.Field<string>("Name"),
Department = v.Field<string>("DepartmentName")
});