LeftOuterJoinedSource.cs

using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using Waher.Persistence.Serialization;
using Waher.Script.Model;
using Waher.Script.Persistence.SQL.Enumerators;
 
namespace Waher.Script.Persistence.SQL.Sources
{
    public class LeftOuterJoinedSource : JoinedSource
    {
        public LeftOuterJoinedSource(IDataSource Left, IDataSource Right, ScriptNode Conditions)
            : base(Left, Right, Conditions)
        {
        }
 
        protected virtual bool Flipped => false;
 
        public override async Task<IResultSetEnumerator> Find(int Offset, int Top, bool Generic, ScriptNode Where, Variables Variables,
            KeyValuePair<VariableReference, bool>[] Order, ScriptNode Node)
        {
            ScriptNode LeftWhere = await Reduce(this.Left, Where);
            KeyValuePair<VariableReference, bool>[] LeftOrder = await Reduce(this.Left, Order);
 
            IResultSetEnumerator e = await this.Left.Find(0, int.MaxValue, Generic, LeftWhere, Variables, LeftOrder, Node);
 
            ScriptNode RightWhere = this.Combine(await Reduce(this.Right, this.Left, Where), this.Conditions);
 
            e = new LeftOuterJoinEnumerator(e, this.Left.Name, this.Right, this.Right.Name, Generic, RightWhere, Variables, this.Flipped);
 
            if (!(Where is null))
                e = new ConditionalEnumerator(e, Variables, Where);
 
            if (Offset > 0)
                e = new OffsetEnumerator(e, Offset);
 
            if (Top != int.MaxValue)
                e = new MaxCountEnumerator(e, Top);
 
            return e;
        }
 
        internal class LeftOuterJoinEnumerator : IResultSetEnumerator
        {
            private readonly IResultSetEnumerator left;
            private readonly IDataSource rightSource;
            private readonly ScriptNode conditions;
            private readonly Variables variables;
            private readonly string leftName;
            private readonly string rightName;
            private readonly bool hasLeftName;
            private readonly bool flipped;
            private readonly bool generic;
            private bool rightFirst;
            private IResultSetEnumerator right;
            private JoinedObject current = null;
            private GenericObject defaultRight = null;
            private ObjectProperties leftVariables = null;
 
            public LeftOuterJoinEnumerator(IResultSetEnumerator Left, string LeftName, IDataSource RightSource, string RightName, 
                bool Generic, ScriptNode Conditions, Variables Variables, bool Flipped)
            {
                this.left = Left;
                this.leftName = LeftName;
                this.rightName = RightName;
                this.rightSource = RightSource;
                this.generic = Generic;
                this.conditions = Conditions;
                this.variables = Variables;
                this.hasLeftName = !string.IsNullOrEmpty(this.leftName);
                this.flipped = Flipped;
            }
 
            public object Current => this.current;
 
            public bool MoveNext()
            {
                return this.MoveNextAsync().Result;
            }
 
            public async Task<bool> MoveNextAsync()
            {
                while (true)
                {
                    if (!(this.right is null))
                    {
                        bool First = this.rightFirst;
                        this.rightFirst = false;
 
                        if (await this.right.MoveNextAsync())
                        {
                            if (this.flipped)
                                this.current = new JoinedObject(this.right.Current, this.rightName, this.left.Current, this.leftName);
                            else
                                this.current = new JoinedObject(this.left.Current, this.leftName, this.right.Current, this.rightName);
 
                            return true;
                        }
                        else
                        {
                            this.right = null;
 
                            if (First)
                            {
                                if (this.defaultRight is null)
                                {
                                    this.defaultRight = new GenericObject(this.rightSource.CollectionName,
                                        typeof(GenericObject).FullName, Guid.Empty, new KeyValuePair<string, object>[0]);
                                }
 
                                if (this.flipped)
                                    this.current = new JoinedObject(this.defaultRight, this.rightName, this.left.Current, this.leftName);
                                else
                                    this.current = new JoinedObject(this.left.Current, this.leftName, this.defaultRight, this.rightName);
 
                                return true;
                            }
                        }
                    }
 
                    if (!await this.left.MoveNextAsync())
                        return false;
 
                    if (this.leftVariables is null)
                        this.leftVariables = new ObjectProperties(this.left.Current, this.variables);
                    else
                        this.leftVariables.Object = this.left.Current;
 
                    if (this.hasLeftName)
                        this.leftVariables[this.leftName] = this.left.Current;
 
                    this.right = await this.rightSource.Find(0, int.MaxValue, this.generic, this.conditions, this.leftVariables, 
                        null, this.conditions);
 
                    this.rightFirst = true;
                }
            }
 
            public void Reset()
            {
                this.current = null;
                this.right = null;
                this.left.Reset();
            }
        }
    
    }
}