文章以efcore 2.0.0-preview2.測試驗證通過。其他版本不保證使用，但是思路不會差太遠。源代碼,報道越短，事情越嚴重！文章越短，內容越精悍！

目標：
1.實現entity的自動發現和mapper設置.
2.默認字符串長度，而不是nvarchar(max).
3.decimal設置精度

實現目標1：繼承RelationalModelCustomizer，重寫Customize方法。

當然，我們也可以重寫dbcontext的OnModelCreating方法，but，我們怎么能這么low呢。必須要用點高級玩意是吧，當然這也是更底層的擴展方式。項目里面有多個dbcontext的話，在這里集中擴展管理比較方便。
在然后，這個RelationalModelCustomizer繼承自ModelCustomizer。在聯想到efcore未來的版本會支持redis，nosql什么的。到時候估計還回有一個osqlModelCustomizer之類的吧，期待中......

實現目標2、3：繼承自CoreConventionSetBuilder類，重寫CreateConventionSet方法。

重寫CreateConventionSet方法，能拿到關鍵的ConventionSet對象。這個對象囊括了諸多的約定配置等等。比如maxlengthattribute屬性標記，stringlength屬性標記，timestamp屬性標記，表id的自動發現規則等等等。。。
那，我們增加2個小小的約定：字符串默認長度（StringDefaultLengthConvention），和decimal精度設置attribute(DecimalPrecisionAttributeConvention)及fluntapi方式.

文章的最后附efcore 所有的可替換擴展service。

//servie,DI注入替換.services.AddSingleton<IModelCustomizer, MyRelationalModelCustomizer>(); services.AddSingleton<ICoreConventionSetBuilder, MyCoreConventionSetBuilder>();
//實現entity的自動發現和mapper設置

public class MyRelationalModelCustomizer : RelationalModelCustomizer{ ?
?public MyRelationalModelCustomizer(ModelCustomizerDependencies dependencies) ? ? ? ?: base(dependencies){} ?
? ?public override void Customize(ModelBuilder modelBuilder, DbContext dbContext) ? ?{ ? ? ?
? ? ?base.Customize(modelBuilder, dbContext); ? ? ?
? ? ? ?var sp = (IInfrastructure<IServiceProvider>)dbContext; ? ?
? ? ? ?? ?var dbOptions = sp.Instance.GetServices<DbContextOptions>(); ? ? ? ?foreach (var item in dbOptions){ ? ? ?
? ? ? ?? ?? ? ?if (item.ContextType == dbContext.GetType())ConfigureDbContextEntityService.Configure(modelBuilder, item, dbContext);}} }

public class MyCoreConventionSetBuilder : CoreConventionSetBuilder{
? ?public MyCoreConventionSetBuilder(CoreConventionSetBuilderDependencies dependencies) : base(dependencies){} ?
? ??public override ConventionSet CreateConventionSet() ? ?{ ? ?
? ??? ?var conventionSet = base.CreateConventionSet(); ? ?
? ??? ?? ?//默認字符串長度，而不是nvarchar(max).//為什么要insert(0,obj),則是因為這個默認規則要最優先處理，如果后續有規則的話就直接覆蓋了。//propertyBuilder.HasMaxLength(32, ConfigurationSource.Convention);//理論上我指定了規則的級別為.Convention，應該和順序就沒有關系了。but，還沒有完成測試，所以我也不知道conventionSet.PropertyAddedConventions.Insert(0, new StringDefaultLengthConvention()); ? ? ? ?//decimal設置精度conventionSet.PropertyAddedConventions.Add(new DecimalPrecisionAttributeConvention()); ? ? ?
? ??? ?? ? ?return conventionSet;} }

下面是StringDefaultLengthConvention和DecimalPrecisionAttributeConvention的實現代碼

//字符串默認長度
public class StringDefaultLengthConvention : IPropertyAddedConvention { ? ?
? ? public InternalPropertyBuilder Apply(InternalPropertyBuilder propertyBuilder) ? ?{ ? ? ?
?if (propertyBuilder.Metadata.ClrType == typeof(string))propertyBuilder.HasMaxLength(32, ConfigurationSource.Convention); ? ?
? ? ?return propertyBuilder;} }
//attribute方式設置decimal精度

public class DecimalPrecisionAttributeConvention : PropertyAttributeConvention<DecimalPrecisionAttribute> { ?
?public override InternalPropertyBuilder Apply(InternalPropertyBuilder propertyBuilder, DecimalPrecisionAttribute attribute, MemberInfo clrMember) ? ?{ ? ? ?
??if (propertyBuilder.Metadata.ClrType == typeof(decimal))propertyBuilder.HasPrecision(attribute.Precision, attribute.Scale); ? ? ?
?? ?return propertyBuilder;}
?? ?/// <summary>
/// decimal類型設置精度
/// </summary>
/// <param name="propertyBuilder"></param>/// <param name="precision">精度</param>/// <param name="scale">小數位數</param>public static PropertyBuilder<TProperty> HasPrecision<TProperty>(this PropertyBuilder<TProperty> propertyBuilder, int precision = 18, int scale = 4) { ? ?//fluntapi方式設置精度 ?((IInfrastructure<InternalPropertyBuilder>)propertyBuilder).Instance.HasPrecision(precision, scale); ?
?? ? ?return propertyBuilder; }
?? ? ?public static InternalPropertyBuilder HasPrecision(this InternalPropertyBuilder propertyBuilder, int precision, int scale){propertyBuilder.Relational(ConfigurationSource.Explicit).HasColumnType($"decimal({precision},{scale})"); ?
?? ? ??return propertyBuilder; }

以上就是實現的代碼，就這么幾行。嗯，還是挺簡單的.

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以下，則是efcore的源代碼。展示了如此之多的可擴展。隨著DI的運用和微軟的開放，嗯。用爛啦，用炸拉(^_^)

//各種規則和約定
public virtual ConventionSet AddConventions(ConventionSet conventionSet){ValueGeneratorConvention valueGeneratorConvention = new RelationalValueGeneratorConvention();ReplaceConvention(conventionSet.BaseEntityTypeChangedConventions, valueGeneratorConvention);ReplaceConvention(conventionSet.PrimaryKeyChangedConventions, valueGeneratorConvention);ReplaceConvention(conventionSet.ForeignKeyAddedConventions, valueGeneratorConvention);ReplaceConvention(conventionSet.ForeignKeyRemovedConventions, valueGeneratorConvention); ?
?var relationalColumnAttributeConvention = new RelationalColumnAttributeConvention();conventionSet.PropertyAddedConventions.Add(relationalColumnAttributeConvention); ?
??var sharedTableConvention = new SharedTableConvention();conventionSet.EntityTypeAddedConventions.Add(new RelationalTableAttributeConvention());conventionSet.EntityTypeAddedConventions.Add(sharedTableConvention);conventionSet.BaseEntityTypeChangedConventions.Add(new DiscriminatorConvention());conventionSet.BaseEntityTypeChangedConventions.Add( ? ?
??? ?new TableNameFromDbSetConvention(Dependencies.Context?.Context, Dependencies.SetFinder));conventionSet.EntityTypeAnnotationChangedConventions.Add(sharedTableConvention);conventionSet.PropertyFieldChangedConventions.Add(relationalColumnAttributeConvention);conventionSet.PropertyAnnotationChangedConventions.Add((RelationalValueGeneratorConvention)valueGeneratorConvention);conventionSet.ForeignKeyUniquenessChangedConventions.Add(sharedTableConvention);conventionSet.ForeignKeyOwnershipChangedConventions.Add(sharedTableConvention);conventionSet.ModelBuiltConventions.Add(new RelationalTypeMappingConvention(Dependencies.TypeMapper));conventionSet.ModelBuiltConventions.Add(sharedTableConvention);conventionSet.ModelAnnotationChangedConventions.Add(new RelationalDbFunctionConvention()); ?
??? ??return conventionSet; } //還是各種規則和約定public virtual ConventionSet CreateConventionSet(){ ?
?var conventionSet = new ConventionSet(); ?
? ?var propertyDiscoveryConvention = new PropertyDiscoveryConvention(Dependencies.TypeMapper); ?
? ? ?var keyDiscoveryConvention = new KeyDiscoveryConvention(); ?
? ? ??var inversePropertyAttributeConvention = new InversePropertyAttributeConvention(Dependencies.TypeMapper);
? ? ??? ?var relationshipDiscoveryConvention = new RelationshipDiscoveryConvention(Dependencies.TypeMapper);conventionSet.EntityTypeAddedConventions.Add(new NotMappedEntityTypeAttributeConvention());conventionSet.EntityTypeAddedConventions.Add(new NotMappedMemberAttributeConvention());conventionSet.EntityTypeAddedConventions.Add(new BaseTypeDiscoveryConvention());conventionSet.EntityTypeAddedConventions.Add(propertyDiscoveryConvention);conventionSet.EntityTypeAddedConventions.Add(keyDiscoveryConvention);conventionSet.EntityTypeAddedConventions.Add(inversePropertyAttributeConvention);conventionSet.EntityTypeAddedConventions.Add(relationshipDiscoveryConvention);conventionSet.EntityTypeAddedConventions.Add(new DerivedTypeDiscoveryConvention());conventionSet.EntityTypeIgnoredConventions.Add(inversePropertyAttributeConvention); ?
? ? ??? ??var foreignKeyIndexConvention = new ForeignKeyIndexConvention(); ? ?var valueGeneratorConvention = new ValueGeneratorConvention();conventionSet.BaseEntityTypeChangedConventions.Add(propertyDiscoveryConvention);conventionSet.BaseEntityTypeChangedConventions.Add(keyDiscoveryConvention);conventionSet.BaseEntityTypeChangedConventions.Add(inversePropertyAttributeConvention);conventionSet.BaseEntityTypeChangedConventions.Add(relationshipDiscoveryConvention);conventionSet.BaseEntityTypeChangedConventions.Add(foreignKeyIndexConvention);conventionSet.BaseEntityTypeChangedConventions.Add(valueGeneratorConvention ); ? ?// An ambiguity might have been resolvedconventionSet.EntityTypeMemberIgnoredConventions.Add(inversePropertyAttributeConvention);conventionSet.EntityTypeMemberIgnoredConventions.Add(relationshipDiscoveryConvention); ?
? ? ??? ???var keyAttributeConvention = new KeyAttributeConvention(); ?
? ? ??? ????var foreignKeyPropertyDiscoveryConvention = new ForeignKeyPropertyDiscoveryConvention(); ?
? ? ??? ???? ?var backingFieldConvention = new BackingFieldConvention(); ? ?var concurrencyCheckAttributeConvention = new ConcurrencyCheckAttributeConvention(); ? ?
? ? ??? ???? ?var databaseGeneratedAttributeConvention = new DatabaseGeneratedAttributeConvention(); ? ?
? ? ??? ???? ?var requiredPropertyAttributeConvention = new RequiredPropertyAttributeConvention(); ?
? ? ??? ???? ? ?var maxLengthAttributeConvention = new MaxLengthAttributeConvention(); ? ?
? ? ??? ???? ? ?var stringLengthAttributeConvention = new StringLengthAttributeConvention(); ?
? ? ??? ???? ? ??var timestampAttributeConvention = new TimestampAttributeConvention();conventionSet.PropertyAddedConventions.Add(backingFieldConvention);conventionSet.PropertyAddedConventions.Add(concurrencyCheckAttributeConvention);conventionSet.PropertyAddedConventions.Add(databaseGeneratedAttributeConvention);conventionSet.PropertyAddedConventions.Add(requiredPropertyAttributeConvention);conventionSet.PropertyAddedConventions.Add(maxLengthAttributeConvention);conventionSet.PropertyAddedConventions.Add(stringLengthAttributeConvention);conventionSet.PropertyAddedConventions.Add(timestampAttributeConvention);conventionSet.PropertyAddedConventions.Add(keyDiscoveryConvention);conventionSet.PropertyAddedConventions.Add(foreignKeyPropertyDiscoveryConvention);conventionSet.PropertyAddedConventions.Add(keyAttributeConvention);conventionSet.PrimaryKeyChangedConventions.Add(valueGeneratorConvention);conventionSet.KeyAddedConventions.Add(foreignKeyPropertyDiscoveryConvention);conventionSet.KeyAddedConventions.Add(foreignKeyIndexConvention);conventionSet.KeyRemovedConventions.Add(foreignKeyPropertyDiscoveryConvention);conventionSet.KeyRemovedConventions.Add(foreignKeyIndexConvention);conventionSet.KeyRemovedConventions.Add(keyDiscoveryConvention); ?
? ? ??? ???? ? ?? ?var cascadeDeleteConvention = new CascadeDeleteConvention();conventionSet.ForeignKeyAddedConventions.Add(new ForeignKeyAttributeConvention(Dependencies.TypeMapper));conventionSet.ForeignKeyAddedConventions.Add(foreignKeyPropertyDiscoveryConvention);conventionSet.ForeignKeyAddedConventions.Add(keyDiscoveryConvention);conventionSet.ForeignKeyAddedConventions.Add(valueGeneratorConvention );conventionSet.ForeignKeyAddedConventions.Add(cascadeDeleteConvention);conventionSet.ForeignKeyAddedConventions.Add(foreignKeyIndexConvention);conventionSet.ForeignKeyRemovedConventions.Add(keyDiscoveryConvention);conventionSet.ForeignKeyRemovedConventions.Add(valueGeneratorConvention );conventionSet.ForeignKeyRemovedConventions.Add(foreignKeyIndexConvention);conventionSet.ForeignKeyUniquenessChangedConventions.Add(foreignKeyPropertyDiscoveryConvention);conventionSet.ForeignKeyUniquenessChangedConventions.Add(foreignKeyIndexConvention);conventionSet.ForeignKeyOwnershipChangedConventions.Add(new NavigationEagerLoadingConvention());conventionSet.ModelBuiltConventions.Add(new ModelCleanupConvention());conventionSet.ModelBuiltConventions.Add(keyAttributeConvention);conventionSet.ModelBuiltConventions.Add(new IgnoredMembersValidationConvention());conventionSet.ModelBuiltConventions.Add(new PropertyMappingValidationConvention(Dependencies.TypeMapper));conventionSet.ModelBuiltConventions.Add(new RelationshipValidationConvention());conventionSet.ModelBuiltConventions.Add(foreignKeyPropertyDiscoveryConvention);conventionSet.NavigationAddedConventions.Add(backingFieldConvention);conventionSet.NavigationAddedConventions.Add(new RequiredNavigationAttributeConvention());conventionSet.NavigationAddedConventions.Add(inversePropertyAttributeConvention);conventionSet.NavigationAddedConventions.Add(foreignKeyPropertyDiscoveryConvention);conventionSet.NavigationAddedConventions.Add(relationshipDiscoveryConvention);conventionSet.NavigationRemovedConventions.Add(relationshipDiscoveryConvention);conventionSet.IndexAddedConventions.Add(foreignKeyIndexConvention);conventionSet.IndexRemovedConventions.Add(foreignKeyIndexConvention);conventionSet.IndexUniquenessChangedConventions.Add(foreignKeyIndexConvention);conventionSet.PropertyNullabilityChangedConventions.Add(cascadeDeleteConvention);conventionSet.PrincipalEndChangedConventions.Add(foreignKeyPropertyDiscoveryConvention);conventionSet.PropertyFieldChangedConventions.Add(keyDiscoveryConvention);conventionSet.PropertyFieldChangedConventions.Add(foreignKeyPropertyDiscoveryConvention);conventionSet.PropertyFieldChangedConventions.Add(keyAttributeConvention);conventionSet.PropertyFieldChangedConventions.Add(concurrencyCheckAttributeConvention);conventionSet.PropertyFieldChangedConventions.Add(databaseGeneratedAttributeConvention);conventionSet.PropertyFieldChangedConventions.Add(requiredPropertyAttributeConvention);conventionSet.PropertyFieldChangedConventions.Add(maxLengthAttributeConvention);conventionSet.PropertyFieldChangedConventions.Add(stringLengthAttributeConvention);conventionSet.PropertyFieldChangedConventions.Add(timestampAttributeConvention); ? ?return conventionSet; }

我就是所有的可替換service啦。不要眼花有點多！，找著合適的用起來！

serviceCollection.AsQueryable().Where(p => p.ServiceType.ToString().StartsWith("Microsoft.EntityFrameworkCore")).Each(sd => {Console.WriteLine($"{sd.Lifetime.ToString().PadRight(15, ' ')}{sd.ServiceType.FullName}"); });

原文地址：http://www.cnblogs.com/calvinK/p/7234872.html

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