AutoMapper源码解析

研究AutoMapper源码前,我们先来看一下AutoMapper的作用

官网解释：AutoMapper是一个简单的小程序库，旨在解决看似复杂的问题-摆脱将一个对象映射到另一个对象的代码解释

首先一个简单的使用AutoMapper方法演示

ar config = new MapperConfiguration(cfg => cfg.CreateMap<ModelObject, ModelDto>());var mapper1 = config.CreateMapper();var mode;= mapper1.Map<ModelObject>(new ModelDto{ Name= 1 });

构造函数

在这段代码中默认创建MapperConfiguration对象,并且传入一个带有映射关系的Action
当MapperConfiguration创建时,会默认执行构造函数

 public MapperConfiguration(MapperConfigurationExpression configurationExpression){_mappers = configurationExpression.Mappers.ToArray();_resolvedMaps = new LockingConcurrentDictionary<TypePair, TypeMap>(GetTypeMap);_executionPlans = new LockingConcurrentDictionary<MapRequest, Delegate>(CompileExecutionPlan);_validator = new ConfigurationValidator(this, configurationExpression);ExpressionBuilder = new ExpressionBuilder(this);ServiceCtor = configurationExpression.ServiceCtor;EnableNullPropagationForQueryMapping = configurationExpression.EnableNullPropagationForQueryMapping ?? false;MaxExecutionPlanDepth = configurationExpression.Advanced.MaxExecutionPlanDepth + 1;ResultConverters = configurationExpression.Advanced.QueryableResultConverters.ToArray();Binders = configurationExpression.Advanced.QueryableBinders.ToArray();RecursiveQueriesMaxDepth = configurationExpression.Advanced.RecursiveQueriesMaxDepth;Configuration = new ProfileMap(configurationExpression);Profiles = new[] { Configuration }.Concat(configurationExpression.Profiles.Select(p => new ProfileMap(p, configurationExpression))).ToArray();configurationExpression.Features.Configure(this);foreach (var beforeSealAction in configurationExpression.Advanced.BeforeSealActions)beforeSealAction?.Invoke(this);Seal();}

在构造函数中实际就是将构建一个MapperConfigurationExpression表达式,然后将当前方法生成Action进行对象的映射,
表达式创建完成之后就进入到AutoMapper核心方法Seal方法
首先我们简单的看一下Seal方法

 private void Seal(){var derivedMaps = new List<Tuple<TypePair, TypeMap>>();var redirectedTypes = new List<Tuple<TypePair, TypePair>>();//获取所有的需要映射的集合 进行注册foreach (var profile in Profiles){//单个进行注册,传入当前对象profile.Register(this);}//IncludeAllDerivedTypes 子类型foreach (var typeMap in _configuredMaps.Values.Where(tm => tm.IncludeAllDerivedTypes)){//循环遍历获取可以赋值的派生类型foreach (var derivedMap in _configuredMaps.Where(tm =>typeMap.SourceType.IsAssignableFrom(tm.Key.SourceType) &&typeMap.DestinationType.IsAssignableFrom(tm.Key.DestinationType) &&typeMap != tm.Value).Select(tm => tm.Value)){//获取派生类型typeMap.IncludeDerivedTypes(derivedMap.SourceType, derivedMap.DestinationType);}}foreach (var profile in Profiles){profile.Configure(this);}foreach (var typeMap in _configuredMaps.Values){_resolvedMaps[typeMap.Types] = typeMap;if (typeMap.DestinationTypeOverride != null){redirectedTypes.Add(Tuple.Create(typeMap.Types, new TypePair(typeMap.SourceType, typeMap.DestinationTypeOverride)));}derivedMaps.AddRange(GetDerivedTypeMaps(typeMap).Select(derivedMap => Tuple.Create(new TypePair(derivedMap.SourceType, typeMap.DestinationType), derivedMap)));}foreach (var redirectedType in redirectedTypes){var derivedMap = FindTypeMapFor(redirectedType.Item2);if (derivedMap != null){_resolvedMaps[redirectedType.Item1] = derivedMap;}}foreach (var derivedMap in derivedMaps.Where(derivedMap => !_resolvedMaps.ContainsKey(derivedMap.Item1))){_resolvedMaps[derivedMap.Item1] = derivedMap.Item2;}foreach (var typeMap in _configuredMaps.Values){typeMap.Seal(this);}Features.Seal(this);}

在这里首先会获取source Type和destination Type的字段映射对象,然后将实现过IProfiles的方法获取到,并且进行注册(添加Mapper关系)

注册

 private void BuildTypeMap(IConfigurationProvider configurationProvider, ITypeMapConfiguration config){//创建类型映射对象//config.SourceType 需要转化的实体//config.DestinationType 被映射的实体// config.IsReverseMap 是否需要反向映射实体var typeMap = TypeMapFactory.CreateTypeMap(config.SourceType, config.DestinationType, this, config.IsReverseMap);config.Configure(typeMap);configurationProvider.RegisterTypeMap(typeMap);}

注册过程就是将需要被转化的实体和被映射的实体注册进TypeMap,最终添加MapperConfigurationExpression表达式中
注册完成之后就是获取到所有的派生类型进行注册

MapperConfigurationExpression表达式解析

当所有的类都已经做好关系映射之后,就进入了 profile.Configure(this)方法,这个方法就是解析MapperConfigurationExpression表达式进行映射。在此之后会进去一些配置映射操作

foreach (var typeMap in _configuredMaps.Values){typeMap.Seal(this);}public void Seal(IConfigurationProvider configurationProvider){if(_sealed){return;}_sealed = true;_inheritedTypeMaps.ForAll(tm => _includedMembersTypeMaps.UnionWith(tm._includedMembersTypeMaps));foreach (var includedMemberTypeMap in _includedMembersTypeMaps){includedMemberTypeMap.TypeMap.Seal(configurationProvider);ApplyIncludedMemberTypeMap(includedMemberTypeMap);}_inheritedTypeMaps.ForAll(tm => ApplyInheritedTypeMap(tm));_orderedPropertyMaps = PropertyMaps.OrderBy(map => map.MappingOrder).ToArray();_propertyMaps.Clear();MapExpression = CreateMapperLambda(configurationProvider, null);Features.Seal(configurationProvider);}

在typeMap.Seal会调用CreateDestinationFunc方法创建一个lambda表达式，内容是new 一个destination对象，在CreateAssignmentFunc方法中会对派生类进行赋值的lambda内容，其中规则就是在注册是使用的规则,但是在两个对象做映射的过程中会有字段没有对应上的属性，CreateMapperFunc会产生一些规则，比如默认值赋值等等。生成的规则会存储在MapExpresion表达式中。

总结

在使用AutoMapper的过程中，系统只会运行一次seal()方法，存储好对象之间的关系，最终调用的时候只会在已经存储好的对象中去寻找映射关系,最终达成映射(ps：当大家在使用过程中,如果不想某些字段进行映射，可以使用IgnoreMapAttribute标记，在配置规则的过程中，如有发现有标记IgnoreMapAttribute的字段，会自动忽略)

如有哪里讲得不是很明白或是有错误，欢迎指正
如您喜欢的话不妨点个赞收藏一下吧