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strategy design pattern
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Claudiu Farcas
+3
-1
@@ -21,6 +21,7 @@ using design_patterns.behavioral.mediator;
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using design_patterns.behavioral.memento;
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using design_patterns.behavioral.observer;
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using design_patterns.behavioral.state;
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using design_patterns.behavioral.strategy;
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namespace design_patterns
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{
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@@ -55,7 +56,8 @@ namespace design_patterns
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// await MediatorSample.Run();
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// await MementoSample.Run();
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// await ObserverSample.Run();
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await StateSample.Run();
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// await StateSample.Run();
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await StrategySample.Run();
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}
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catch (System.Exception ex)
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{
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@@ -0,0 +1,283 @@
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using System.Linq.Expressions;
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using System.Linq;
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using System.Text;
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using System;
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using System.Threading.Tasks;
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using System.Collections.Generic;
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namespace design_patterns.behavioral.strategy
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{
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/// <summary>
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/// Strategy is a behavioral design pattern that lets you
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/// define a family of algorithms, put each of them into a separate class,
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/// and make their objects interchangeable.
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///
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/// Use it when:
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/// - you want to use different variants of an algorithm
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/// within an object and be able to switch from one algorithm
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/// to another during runtime.
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/// - you have a lot of similar classes that only differ
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/// in the way they execute some behavior.
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/// - to isolate the business logic of a class from the
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/// implementation details of algorithms that may not be as important
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/// in the context of that logic.
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/// - your class has a massive conditional operator that switches
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/// between different variants of the same algorithm.
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/// </summary>
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public class StrategySample
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{
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public static async Task Run()
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{
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Console.WriteLine("Behavioral - Strategy");
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var processor = new SqlBuilderProcessor(new SqliteStrategy());
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processor.Select.AddRange(new string[]{"fieldA", "fieldB" });
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processor.From = "TableABC";
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processor.Where = new LogicExpression {
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First = new LogicExpression {
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First = "fieldF",
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Operator = LogicOperator.Equal,
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Last = 1
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},
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Operator = LogicOperator.And,
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Last = true
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};
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processor.Orderby.Add(("fieldA", OrderDirection.ASC));
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processor.Orderby.Add(("fieldC", OrderDirection.DESC));
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System.Console.WriteLine(processor);
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// second strategy
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processor.SetStrategy(new MsSqlStrategy());
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System.Console.WriteLine(processor);
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}
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public interface ISqlStrategy {
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string Select(IProcessor processor);
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string From(IProcessor processor);
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string Where(IProcessor processor);
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string OrderBy(IProcessor processor);
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string GetOperatorSymbol(LogicOperator op);
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}
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public enum OrderDirection {
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ASC,
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DESC
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}
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public enum LogicOperator {
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And,
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Or,
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Not,
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Like,
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Greater,
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Less,
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Equal,
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NotEqual
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}
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public class LogicExpression
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{
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public object First { get; set; }
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public StrategySample.LogicOperator Operator { get; set; }
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public object Last { get; set; }
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private StringBuilder sb = new StringBuilder();
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private Func<LogicOperator, string> operatorFunc;
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private Func<object, string> fieldFunc;
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public string GetWhereString(Func<object, string> fieldFunc, Func<LogicOperator, string> operatorFunc) {
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sb.Clear();
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this.fieldFunc = fieldFunc;
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this.operatorFunc = operatorFunc;
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GetCondition(this);
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if(sb.Length>0)
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sb.Insert(0, "WHERE ");
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return sb.ToString();
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}
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private void GetCondition(LogicExpression where){
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ProcessExpressionTerm(where.First);
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sb.Append($" {operatorFunc(where.Operator)} ");
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ProcessExpressionTerm(where.Last);
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}
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private void ProcessExpressionTerm(object expterm) {
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if(expterm is LogicExpression newWhere) {
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// recursive call
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sb.Append("(");
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GetCondition(newWhere);
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sb.Append(")");
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}
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else {
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sb.Append(fieldFunc(expterm));
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}
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}
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}
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public interface IProcessor {
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void SetStrategy(ISqlStrategy strategy);
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List<string> Select { get; }
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string From { get; }
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List<(string, OrderDirection)> Orderby { get; }
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LogicExpression Where { get; }
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}
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public class SqlBuilderProcessor : IProcessor {
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private ISqlStrategy strategy;
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public SqlBuilderProcessor (ISqlStrategy strategy) {
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this.strategy = strategy;
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}
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public List<string> Select { get; internal set; } = new List<string>();
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public string From { get; set; }
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public List<(string, OrderDirection)> Orderby { get; } = new List<(string, OrderDirection)>();
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// public Expression Where { get; }
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public LogicExpression Where { get; set; }
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public override string ToString()
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{
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StringBuilder sb = new StringBuilder();
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sb.Append(strategy.Select(this));
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sb.Append(" ");
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sb.Append(strategy.From(this));
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sb.Append(" ");
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sb.Append(strategy.Where(this));
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sb.Append(" ");
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sb.Append(strategy.OrderBy(this));
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return sb.ToString();
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}
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public void SetStrategy(ISqlStrategy strategy)
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{
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this.strategy = strategy;
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}
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}
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public class SqliteStrategy : ISqlStrategy
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{
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public string From(IProcessor processor)
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{
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return $"FROM {processor.From}";
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}
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public string OrderBy(IProcessor processor)
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{
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if(processor.Orderby.Any())
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{
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var orderby = string.Join(", ",
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processor.Orderby.Select((f,d) => {
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return ((OrderDirection)d == OrderDirection.ASC ?
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$"{f.Item1} ASC" :
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$"{f.Item1} DESC");
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}).ToArray());
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return $"ORDER BY {orderby}";
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}
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return string.Empty;
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}
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public string Select(IProcessor processor)
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{
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if(processor.Select.Any())
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return $"SELECT {string.Join(", ", processor.Select)}";
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return "SELECT *";
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}
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// StringBuilder sb = new StringBuilder();
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public string Where(IProcessor processor)
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{
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var whereString = processor.Where.GetWhereString(f => $"{f}", l => GetOperatorSymbol(l));
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if(whereString.Length>0)
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return $"WHERE {whereString}";
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return string.Empty;
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}
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public string GetOperatorSymbol(LogicOperator op)
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{
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switch (op)
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{
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case LogicOperator.Equal:
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return "=";
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case LogicOperator.NotEqual:
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return "<>";
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case LogicOperator.Greater:
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return ">";
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case LogicOperator.Less:
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return "<";
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case LogicOperator.And:
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return "AND";
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case LogicOperator.Or:
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return "OR";
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default:
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break;
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}
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return string.Empty;
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}
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}
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public class MsSqlStrategy : ISqlStrategy
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{
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public string From(IProcessor processor)
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{
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return $"FROM [{processor.From}]";
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}
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public string GetOperatorSymbol(LogicOperator op)
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{
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switch (op)
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{
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case LogicOperator.Equal:
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return "==";
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case LogicOperator.NotEqual:
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return "!=";
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case LogicOperator.Greater:
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return ">";
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case LogicOperator.Less:
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return "<";
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case LogicOperator.And:
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return "And";
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case LogicOperator.Or:
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return "Or";
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default:
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break;
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}
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return string.Empty;
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}
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public string OrderBy(IProcessor processor)
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{
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if(processor.Orderby.Any())
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{
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var orderby = string.Join(", ",
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processor.Orderby.Select((f,d) => {
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return ((OrderDirection)d == OrderDirection.ASC ?
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$"[{f.Item1}] ASC" :
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$"[{f.Item1}] DESC");
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}).ToArray());
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return $"ORDER BY {orderby}";
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}
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return string.Empty;
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}
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public string Select(IProcessor processor)
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{
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if(processor.Select.Any())
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return $"SELECT {string.Join(", ", processor.Select.Select(f => $"[{f}]"))}";
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return "SELECT *";
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}
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public string Where(IProcessor processor)
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{
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var whereString = processor.Where.GetWhereString(f => $"[{f}]", l => GetOperatorSymbol(l));
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if(whereString.Length>0)
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return $"WHERE {whereString}";
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return string.Empty;
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}
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}
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}
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}
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