Revenj.DatabasePersistence.Postgres.QueryGeneration.QueryComposition.QueryParts.GetFromPart C# (CSharp) Method

        public string GetFromPart()
        {
            if (MainFrom == null)
                throw new InvalidOperationException("A query must have a from part");

            var sb = new StringBuilder();

            if (AdditionalJoins.Any(it => EndsWithQuerySource(it.FromExpression as MemberExpression)))
                sb.AppendFormat("FROM ({0}) sq ", GetInnerFromPart());
            else
                sb.AppendFormat("FROM {0}", GetQuerySourceFromExpression(MainFrom.ItemName, MainFrom.ItemType, MainFrom.FromExpression));

            var emptyJoins =
                (from j in AdditionalJoins
                 let sqe = j.FromExpression as SubQueryExpression
                 where sqe != null
                 && sqe.QueryModel.ResultOperators.Count == 1
                 && sqe.QueryModel.ResultOperators[0] is DefaultIfEmptyResultOperator
                 select new { j, sqe })
                 .ToList();

            var groupPairs =
                (from aj in emptyJoins
                 let mfe = aj.sqe.QueryModel.MainFromClause.FromExpression as QuerySourceReferenceExpression
                 where mfe != null
                 select new { aj.j, g = mfe.ReferencedQuerySource })
                 .ToList();

            foreach (var aj in AdditionalJoins)
            {
                var me = aj.FromExpression as MemberExpression;
                if (EndsWithQuerySource(me))
                    continue;
                if (groupPairs.Any(it => it.j == aj))
                    continue;
                var ej = emptyJoins.Find(it => it.j == aj);
                if (ej != null)
                {
                    var qm = ej.sqe.QueryModel;
                    var sel = qm.SelectClause.Selector as QuerySourceReferenceExpression;
                    if (sel != null && sel.ReferencedQuerySource.Equals(qm.MainFromClause) && qm.BodyClauses.Count > 0)
                    {
                        var wc = qm.BodyClauses.Where(it => it is WhereClause).Cast<WhereClause>().ToList();
                        if (wc.Count == qm.BodyClauses.Count)
                        {
                            var mfc = qm.MainFromClause;
                            mfc.ItemName = aj.ItemName;
                            sb.AppendFormat("{0}	LEFT JOIN {1} ON {2}",
                                Environment.NewLine,
                                GetQuerySourceFromExpression(mfc.ItemName, mfc.ItemType, mfc.FromExpression),
                                string.Join(" AND ", wc.Select(it => GetSqlExpression(it.Predicate))));
                            continue;
                        }
                    }
                }
                sb.AppendFormat("{0}	CROSS JOIN {1}",
                    Environment.NewLine,
                    GetQuerySourceFromExpression(aj.ItemName, aj.ItemType, aj.FromExpression));
            }
            foreach (var j in Joins)
            {
                sb.AppendFormat("{0}	INNER JOIN {1} ON ({2}) = ({3}){0}",
                    Environment.NewLine,
                    GetQuerySourceFromExpression(j.ItemName, j.ItemType, j.InnerSequence),
                    GetSqlExpression(j.InnerKeySelector),
                    GetSqlExpression(j.OuterKeySelector));
            }
            foreach (var gj in GroupJoins)
            {
                var aj = groupPairs.FirstOrDefault(it => it.g == gj);
                if (aj == null)
                    throw new FrameworkException("Can't find group join part!");
                gj.ItemName = aj.j.ItemName;
                gj.JoinClause.ItemName = aj.j.ItemName;
                sb.AppendFormat("{0}	LEFT JOIN {1} ON ({2}) = ({3}){0}",
                    Environment.NewLine,
                    GetQuerySourceFromExpression(gj.ItemName, gj.ItemType, gj.JoinClause.InnerSequence),
                    GetSqlExpression(gj.JoinClause.InnerKeySelector),
                    GetSqlExpression(gj.JoinClause.OuterKeySelector));
            }

            sb.AppendLine();
            return sb.ToString();
        }