Reflection in C# Case studies in metaprogramming. torsdag 6 mars 14

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Gervais Morgan
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1 Reflection in C# Case studies in metaprogramming

2 GenericDAO

3 ORM for legacy DB DB with T-SQL Stored Procedures (SP) Apps written in C#, VB.Net and VB6 Domain classes require mapping classes Different SP:s return different sets of data for the same domain objects Related data..

4 1 Domain class - 1 DAO Interface Layer UI Model Service Layer Data Access Layer Domain Model Database

5 1 Domain class - 1 DAO Interface Layer UI Model Service Layer Data Access Layer Domain Model Database

6 1 Domain class - 1 DAO Interface Layer UI Model LoginService login(string user) logout(string user) Service Layer Data Access Layer Domain Model Person firstname lastname employments address PersonDAO getall() get(int id) getbyusername(string username)... SQL query tabulated result sets Database DB

7 1 Domain class - 1 DAO Interface Layer UI Model LoginService login(string user) logout(string user) Service Layer Data Access Layer Domain Model Person firstname lastname employments address PersonDAO getall() get(int id) getbyusername(string username)... SQL query Database tabulated result sets Grade grade date Course code credits teacher students GradeDAO getall() get(int id) getby(string studentname, string coursename)... CourseDAO getall() get(int id) getbyname(string coursename)... DB

8 Related data var people = new PersonDAO().GetAll() Person firstname: "Ola" lastname: "Leifler" employments address null null Person firstname: "Berit" lastname: "Larsson" employments address null null people.selectmany(p => p.employments) Do we know if employments have been fetched? What if we only want to make one DB call? (Select 1+N Problem)

9 Legacy support Person firstname lastname employments address PersonDAO getall() get(int id) getbyemployment(int id) getwithaddress(int id) "getall" DB fname: "Ola" lname: "Leifler" fname: "Berit" lname: "Jansson" PersonDAO getall() get(int id) getbyemployment(int id) getwithaddress(int id) "getwithaddress" DB firstname: "Ola" llastname: "Leifler" streetaddress: "Storgatan 1" city: "Linköping"

10 Legacy support Person firstname lastname employments address PersonDAO getall() get(int id) getbyemployment(int id) getwithaddress(int id) "getall" DB fname: "Ola" lname: "Leifler" fname: "Berit" lname: "Jansson" PersonDAO getall() get(int id) getbyemployment(int id) getwithaddress(int id) "getwithaddress" DB firstname: "Ola" llastname: "Leifler" streetaddress: "Storgatan 1" city: "Linköping"

11 Legacy support Person firstname lastname employments address PersonDAO getall() get(int id) getbyemployment(int id) getwithaddress(int id) "getall" DB Address streetaddress city fname: "Ola" lname: "Leifler" fname: "Berit" lname: "Jansson" PersonDAO getall() get(int id) getbyemployment(int id) getwithaddress(int id) "getwithaddress" DB firstname: "Ola" llastname: "Leifler" streetaddress: "Storgatan 1" city: "Linköping"

12 Solution 1 Generic Data Access Object class Dynamic name resolution of Stored Procedures Generated proxy classes for lazy loading Markup and configuration to configure loading related objects, and mapping between data fields and class properties

13 1 Generic DAO var people = GenericDAO<Domain.Person>.Get("GetPeopleByRole", new { RoleId = 3 ); people.should().notbeempty();

14 1 Generic DAO var people = GenericDAO<Domain.Person>.Get("GetPeopleByRole", new { RoleId = 3 ); people.should().notbeempty(); private static ICollection<T> GetEntities(string procedurename,object parameterobject, int limit) { int recordsread=0; var config=getconfig(procedurename); IList<T> entities=new ConcurrentList<T>(); try { using(dbcommand command=buildcommand(procedurename,parameterobject)) { using(idatareader reader=command.executereader()) { var fieldnames=reader.names(); config.init(command,fieldnames); var allfieldsused=config.getallfieldsusedby(reader); if((config.policy& GenericDAO.ExceptionPolicy.AbortOnFieldsUnused)!=0&&!fieldNames.IsSubSetOf(allFieldsUsed)) { // Abort if some SQL result fields are unused throw new FieldsUnusedFromQueryException(fieldNames.Except(allFieldsUsed)); // Add a mapping from the SP to the properties it can set on the current object while(reader.read()&&++recordsread<limit) { entities.add(config.injectfrom(reader)); entities=config.process(entities); finally { DBAccess.CloseConnection(); return entities;

15 1 Generic DAO var people = GenericDAO<Domain.Person>.Get("GetPeopleByRole", new { RoleId = 3 ); people.should().notbeempty(); private static ICollection<T> GetEntities(string procedurename,object parameterobject, int limit) { int recordsread=0; var config=getconfig(procedurename); IList<T> entities=new ConcurrentList<T>(); try { using(dbcommand command=buildcommand(procedurename,parameterobject)) { using(idatareader reader=command.executereader()) { var fieldnames=reader.names(); config.init(command,fieldnames); var allfieldsused=config.getallfieldsusedby(reader); if((config.policy& GenericDAO.ExceptionPolicy.AbortOnFieldsUnused)!=0&&!fieldNames.IsSubSetOf(allFieldsUsed)) { // Abort if some SQL result fields are unused throw new FieldsUnusedFromQueryException(fieldNames.Except(allFieldsUsed)); // Add a mapping from the SP to the properties it can set on the current object while(reader.read()&&++recordsread<limit) { entities.add(config.injectfrom(reader)); entities=config.process(entities); finally { DBAccess.CloseConnection(); return entities;

16 1 Generic DAO var people = GenericDAO<Domain.Person>.Get("GetPeopleByRole", new { RoleId = 3 ); people.should().notbeempty(); private static ICollection<T> GetEntities(string procedurename,object parameterobject, int limit) { int recordsread=0; var config=getconfig(procedurename); IList<T> entities=new ConcurrentList<T>(); try { using(dbcommand command=buildcommand(procedurename,parameterobject)) { using(idatareader reader=command.executereader()) { var fieldnames=reader.names(); config.init(command,fieldnames); var allfieldsused=config.getallfieldsusedby(reader); if((config.policy& GenericDAO.ExceptionPolicy.AbortOnFieldsUnused)!=0&&!fieldNames.IsSubSetOf(allFieldsUsed)) { // Abort if some SQL result fields are unused throw new FieldsUnusedFromQueryException(fieldNames.Except(allFieldsUsed)); // Add a mapping from the SP to the properties it can set on the current object while(reader.read()&&++recordsread<limit) { entities.add(config.injectfrom(reader)); entities=config.process(entities); finally { DBAccess.CloseConnection(); return entities;

17 Dynamic name resolution

18 Dynamic name resolution GetAll() GetPeopleByRole() x 500

19 Dynamic name resolution GetAll() GetPeopleByRole() x 500 GetAll GetPeopleByRole x 500

20 Dynamic name resolution GetAll() GetPeopleByRole() x 500 GetAll GetPeopleByRole x 500

21 Dynamic name resolution using System; using System.Collections.Generic; using System.Linq; using System.Dynamic; using Configuration; using Extensions; GetAll() GetPeopleByRole() x 500 GetAll GetPeopleByRole x 500 namespace Core { public class Dispatcher<T>:DynamicObject where T:class, new() { [... ] public override bool TryInvokeMember(InvokeMemberBinder binder, object[] args, out object result) { string procedurename=binder.name; object paramobj=getparameterobject(binder,args); string storedprocedurename=genericdao<t>.storedprocedurefullname(procedurename); if(procedurename.startswith("get")) { result=getresult(paramobj,storedprocedurename); [... ]

22 Dynamic name resolution using System; using System.Collections.Generic; using System.Linq; using System.Dynamic; using Configuration; using Extensions; GetAll() GetPeopleByRole() x 500 GetAll GetPeopleByRole x 500 namespace Core { public class Dispatcher<T>:DynamicObject where T:class, new() { [... ] public override bool TryInvokeMember(InvokeMemberBinder binder, object[] args, out object result) { string procedurename=binder.name; object paramobj=getparameterobject(binder,args); string storedprocedurename=genericdao<t>.storedprocedurefullname(procedurename); if(procedurename.startswith("get")) { result=getresult(paramobj,storedprocedurename); [... ]

23 Dynamic name resolution using System; using System.Collections.Generic; using System.Linq; using System.Dynamic; using Configuration; using Extensions; GetAll() GetPeopleByRole() x 500 GetAll GetPeopleByRole x 500 namespace Core { public class Dispatcher<T>:DynamicObject where T:class, new() { [... ] public override bool TryInvokeMember(InvokeMemberBinder binder, object[] args, out object result) { string procedurename=binder.name; object paramobj=getparameterobject(binder,args); string storedprocedurename=genericdao<t>.storedprocedurefullname(procedurename); if(procedurename.startswith("get")) { result=getresult(paramobj,storedprocedurename); [... ] dynamic dao = GenericDAO<Domain.Person>.Dispatch(); IEnumerable<Domain.Person> people = dao.getpeoplebyrole(roleid: 3); people.should().notbeempty();

24 Dynamic name resolution using System; using System.Collections.Generic; using System.Linq; using System.Dynamic; using Configuration; using Extensions; GetAll() GetPeopleByRole() x 500 GetAll GetPeopleByRole x 500 namespace Core { public class Dispatcher<T>:DynamicObject where T:class, new() { [... ] public override bool TryInvokeMember(InvokeMemberBinder binder, object[] args, out object result) { string procedurename=binder.name; object paramobj=getparameterobject(binder,args); string storedprocedurename=genericdao<t>.storedprocedurefullname(procedurename); if(procedurename.startswith("get")) { result=getresult(paramobj,storedprocedurename); [... ] dynamic dao = GenericDAO<Domain.Person>.Dispatch(); IEnumerable<Domain.Person> people = dao.getpeoplebyrole(roleid: 3); people.should().notbeempty();

25 Generated proxy classes protected internal T CreateObject<T>(IDataReader reader, IEnumerable<string> allowedfields=null) where T:class, new() { T proxy=proxygenerator.createclassproxy<t>(proxygenerationoptions, new LazyLoadingInterceptor<T>()); foreach(var fieldandproperty in GetFieldsToPropertiesMap<T>(reader, allowedfields)) { var value=getvalue(reader[fieldandproperty.key], fieldandproperty.value); if(value!=null) { GetSetter(fieldAndProperty.Value)(proxy, value); return proxy;

26 Generated proxy classes protected internal T CreateObject<T>(IDataReader reader, IEnumerable<string> allowedfields=null) where T:class, new() { T proxy=proxygenerator.createclassproxy<t>(proxygenerationoptions, new LazyLoadingInterceptor<T>()); foreach(var fieldandproperty in GetFieldsToPropertiesMap<T>(reader, allowedfields)) { var value=getvalue(reader[fieldandproperty.key], fieldandproperty.value); if(value!=null) { GetSetter(fieldAndProperty.Value)(proxy, value); return proxy;

27 Generated proxy classes namespace Support { public class LazyLoadingInterceptor<T>:BaseInterceptor,IInterceptor where T:class, new() { [... ] public void Intercept(IInvocation invocation) { object proxy=invocation.proxy; // Get the target property access method var target=invocation.methodinvocationtarget; string propertyname=getpropertyname(target.name); if(target.name.startswith("get_")) { if(!ispropertyloaded(propertyname)) { // Ignore the returned enumeration of elements from Prefetcher<T> as it is just the original sequence with properties set Prefetcher<T>.FetchRelatedProperty(new List<T>() { proxy as T,typeof(T).GetProperty(propertyName)); SetPropertyLoaded(propertyName); else { // Setter invocation: update "property loaded" map with indication of whether non-default value set var settervalue=invocation.getargumentvalue(0); SetPropertyLoaded(propertyName,setterValue!=setterValue.GetType().DefaultValue()); invocation.proceed();

28 Generated proxy classes namespace Support { public class LazyLoadingInterceptor<T>:BaseInterceptor,IInterceptor where T:class, new() { [... ] public void Intercept(IInvocation invocation) { object proxy=invocation.proxy; // Get the target property access method var target=invocation.methodinvocationtarget; string propertyname=getpropertyname(target.name); if(target.name.startswith("get_")) { if(!ispropertyloaded(propertyname)) { // Ignore the returned enumeration of elements from Prefetcher<T> as it is just the original sequence with properties set Prefetcher<T>.FetchRelatedProperty(new List<T>() { proxy as T,typeof(T).GetProperty(propertyName)); SetPropertyLoaded(propertyName); else { // Setter invocation: update "property loaded" map with indication of whether non-default value set var settervalue=invocation.getargumentvalue(0); SetPropertyLoaded(propertyName,setterValue!=setterValue.GetType().DefaultValue()); invocation.proceed(); Intercept dynamically intercepts method invocations so that properties that are not loaded are fetched from the database

29 Markup and configuration " " public String Name { get; set; " " public String Age { get; set; " " [SP("emp_GetEmployment")] " " [ForeignKey("PersonId")] " " public virtual ICollection<Employment> Employments { get; set;

30 Markup and configuration " " public String Name { get; set; " " public String Age { get; set; " " [SP("emp_GetEmployment")] " " [ForeignKey("PersonId")] " " public virtual ICollection<Employment> Employments { get; set;

31 Markup and configuration " " public String Name { get; set; " " public String Age { get; set; " " [SP("emp_GetEmployment")] " " [ForeignKey("PersonId")] " " public virtual ICollection<Employment> Employments { get; set;

32 Markup and configuration " " public String Name { get; set; " " public String Age { get; set; " " [SP("emp_GetEmployment")] " " [ForeignKey("PersonId")] " " public virtual ICollection<Employment> Employments { get; set;

33 Markup and configuration GenericDAO<Person>.Configure("per_GetPeopleWithAddress").By(x => { x.scanforrelatedtypes(genericdao.fetchrelatedobjectspolicy.scanfields); ); Scan result set for field names that match properties of related objects

34 Markup and configuration GenericDAO<Person>.Configure("GetPeopleByRole").By(x => { x.map("perid").to(p => p.id); x.include<contactinfo>().by(y => { y.map("contactprivateid").to(c => c.id); y.map("privatemobile").to(c => c.mobile); y.map("private ").to(c => c. ); y.through(p => p.privatecontact); ); x.include<contactinfo>().by(y => { y.map("contactcompanyid").to(c => c.id); y.map("companymobile").to(c => c.mobile); y.map("company ").to(c => c. ); y.through(p => p.companycontact); ); x.include<address>(); ); Map each row in the result set to a main Person object, 2x ContactInfo and an Address

35 Markup and configuration per_getpersonsbyrole()

36 Markup and configuration per_getpersonsbyrole() PerId ContactPrivateId PrivateMobile Private ContactCompanyId CompanyMobile Company john@apple.com apple@john.com Id StreetAddress City 20 1 Infinite loop Götene

37 Markup and configuration per_getpersonsbyrole() PerId ContactPrivateId PrivateMobile Private ContactCompanyId CompanyMobile Company john@apple.com apple@john.com Id StreetAddress City 20 1 Infinite loop Götene Person Id: 3 PrivateContact CompanyContact Address ContactInfo Id:14 Mobile: " " "john@apple.com" ContactInfo Id: 15 Mobile: " " "apple@john.com" Address Id: 20 StreetAddress: "1 Infinite loop" City: "Götene"

38 Markup and configuration per_getpersonsbyrole() PerId ContactPrivateId PrivateMobile Private ContactCompanyId CompanyMobile Company john@apple.com apple@john.com Id StreetAddress City 20 1 Infinite loop Götene Person Id: 3 PrivateContact CompanyContact Address ContactInfo Id:14 Mobile: " " "john@apple.com" ContactInfo Id: 15 Mobile: " " "apple@john.com" Address Id: 20 StreetAddress: "1 Infinite loop" City: "Götene"

39 Markup and configuration y.map("contactcompanyid").to(c => c.id);

40 Markup and configuration y.map("contactcompanyid").to(c => c.id); public void To<T1>(Expression<Func<T,T1>> propertyselector) { var selectorexpression = (MemberExpression) propertyselector.body; var prop = (PropertyInfo) selectorexpression.member; Configurator.CustomFieldsToPropertiesMap[FieldName]=prop;

41 Markup and configuration y.map("contactcompanyid").to(c => c.id); public void To<T1>(Expression<Func<T,T1>> propertyselector) { var selectorexpression = (MemberExpression) propertyselector.body; var prop = (PropertyInfo) selectorexpression.member; Configurator.CustomFieldsToPropertiesMap[FieldName]=prop; FieldName is the name of the field returned in the result set (ContactCompanyId)

43 Expression Generation

44 public Expression<Func<T,Boolean>> CreateFilterExpression<T>(params T[] args) { var x = "x"; var paramexp = Expression.Parameter(typeof(T), x); Expression t = Expression.Constant(false); return Expression.Lambda<Func<T,Boolean>>(args.Aggregate(t, " " " " " " " (expr, arg) => " " " " " " " Expression.OrElse(Expression.Equal(paramExp, Expression.Constant(arg)), " " " " " " " " " expr)), " " " " " new ParameterExpression[] { paramexp );

45 Return an expression tree that accepts T and returns a boolean public Expression<Func<T,Boolean>> CreateFilterExpression<T>(params T[] args) { var x = "x"; var paramexp = Expression.Parameter(typeof(T), x); Expression t = Expression.Constant(false); return Expression.Lambda<Func<T,Boolean>>(args.Aggregate(t, " " " " " " " (expr, arg) => " " " " " " " Expression.OrElse(Expression.Equal(paramExp, Expression.Constant(arg)), " " " " " " " " " expr)), " " " " " new ParameterExpression[] { paramexp );

46 public Expression<Func<T,Boolean>> CreateFilterExpression<T>(params T[] args) { var x = "x"; var paramexp = Expression.Parameter(typeof(T), x); Node that refers to the parameter x Expression t = Expression.Constant(false); return Expression.Lambda<Func<T,Boolean>>(args.Aggregate(t, " " " " " " " (expr, arg) => " " " " " " " Expression.OrElse(Expression.Equal(paramExp, Expression.Constant(arg)), " " " " " " " " " expr)), " " " " " new ParameterExpression[] { paramexp );

47 public Expression<Func<T,Boolean>> CreateFilterExpression<T>(params T[] args) { var x = "x"; var paramexp = Expression.Parameter(typeof(T), x); Expression t = Expression.Constant(false); Node that refers to the constant false return Expression.Lambda<Func<T,Boolean>>(args.Aggregate(t, " " " " " " " (expr, arg) => " " " " " " " Expression.OrElse(Expression.Equal(paramExp, Expression.Constant(arg)), " " " " " " " " " expr)), " " " " " new ParameterExpression[] { paramexp );

48 public Expression<Func<T,Boolean>> CreateFilterExpression<T>(params T[] args) { var x = "x"; var paramexp = Expression.Parameter(typeof(T), x); Expression t = Expression.Constant(false); return Expression.Lambda<Func<T,Boolean>>(args.Aggregate(t, " " " " " " " (expr, arg) => " " " " " " " Expression.OrElse(Expression.Equal(paramExp, Expression.Constant(arg)), " " " " " " " " " expr)), " " " " " new ParameterExpression[] { paramexp ); x == arg

49 public Expression<Func<T,Boolean>> CreateFilterExpression<T>(params T[] args) { var x = "x"; var paramexp = Expression.Parameter(typeof(T), x); Expression t = Expression.Constant(false); return Expression.Lambda<Func<T,Boolean>>(args.Aggregate(t, " " " " " " " (expr, arg) => " " " " " " " Expression.OrElse(Expression.Equal(paramExp, Expression.Constant(arg)), " " " " " " " " " expr)), " " " " " new ParameterExpression[] { paramexp ); for all values of arg in args

50 public Expression<Func<T,Boolean>> CreateFilterExpression<T>(params T[] args) { var x = "x"; var paramexp = Expression.Parameter(typeof(T), x); Expression t = Expression.Constant(false); return Expression.Lambda<Func<T,Boolean>>(args.Aggregate(t, " " " " " " " (expr, arg) => " " " " " " " Expression.OrElse(Expression.Equal(paramExp, Expression.Constant(arg)), " " " " " " " " " expr)), " " " " " new ParameterExpression[] { paramexp ); combined with (OrElse)

51 public Expression<Func<T,Boolean>> CreateFilterExpression<T>(params T[] args) { var x = "x"; var paramexp = Expression.Parameter(typeof(T), x); Expression t = Expression.Constant(false); return Expression.Lambda<Func<T,Boolean>>(args.Aggregate(t, " " " " " " " (expr, arg) => " " " " " " " Expression.OrElse(Expression.Equal(paramExp, Expression.Constant(arg)), " " " " " " " " " expr)), " " " " " new ParameterExpression[] { paramexp );

TDDB84: Lecture 09. SOLID, Language design, Summary. fredag 11 oktober 13

TDDB84: Lecture 09. SOLID, Language design, Summary. fredag 11 oktober 13 TDDB84: Lecture 09 SOLID, Language design, Summary SOLID Single responsibility principle Open/closed principle Liskov substitution principle Interface segregation principle Depency inversion principle