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Entity Framework Code First -- 延迟加载和预先加载

2013-09-18 12:46 351 查看

还是以这两个表为例子

country包含零个或多个city，这个外键关系是我后来加上去，原来没有。然后再用PowerTool逆向，产生如下代码

usingSystem.ComponentModel.DataAnnotations.Schema;

[code]usingSystem.Data.Entity.ModelConfiguration;

namespaceEFEntity.Models.Mapping

publicclasscityMap:EntityTypeConfiguration<city>

publiccityMap()

//PrimaryKey

this.HasKey(t=>t.ID);

//Properties

this.Property(t=>t.Name)

.IsRequired()

.HasMaxLength(35);

this.Property(t=>t.CountryCode)

.IsRequired()

.HasMaxLength(3);

this.Property(t=>t.District)

.IsRequired()

.HasMaxLength(20);

//Table&ColumnMappings

this.ToTable("city","world");

this.Property(t=>t.ID).HasColumnName("ID");

this.Property(t=>t.Name).HasColumnName("Name");

this.Property(t=>t.CountryCode).HasColumnName("CountryCode");

this.Property(t=>t.District).HasColumnName("District");

this.Property(t=>t.Population).HasColumnName("Population");

//Relationships//这里加了一个关系this.HasRequired(t=>t.country)//这个指向city模型的publicvirtualcountrycountry{get;set;}.WithMany(t=>t.cities)//这个指向country模型的publicvirtualICollection<city>cities{get;set;}.HasForeignKey(d=>d.CountryCode);//这个指向city模型的publicstringCountryCode{get;set;}

[/code]

以上是city映射，下面是country映射

usingSystem.ComponentModel.DataAnnotations.Schema;

usingSystem.Data.Entity.ModelConfiguration;

namespaceEFEntity.Models.Mapping

publicclasscountryMap:EntityTypeConfiguration<country>

publiccountryMap()

//PrimaryKey

this.HasKey(t=>t.Code);

//Properties

this.Property(t=>t.Code)

.IsRequired()

.HasMaxLength(3);

this.Property(t=>t.Name)

.IsRequired()

.HasMaxLength(52);

this.Property(t=>t.Continent)

.IsRequired()

.HasMaxLength(65532);

this.Property(t=>t.Region)

.IsRequired()

.HasMaxLength(26);

this.Property(t=>t.LocalName)

.IsRequired()

.HasMaxLength(45);

this.Property(t=>t.GovernmentForm)

.IsRequired()

.HasMaxLength(45);

this.Property(t=>t.HeadOfState)

.HasMaxLength(60);

this.Property(t=>t.Code2)

.IsRequired()

.HasMaxLength(2);

//Table&ColumnMappings

this.ToTable("country","world");

this.Property(t=>t.Code).HasColumnName("Code");

this.Property(t=>t.Name).HasColumnName("Name");

this.Property(t=>t.Continent).HasColumnName("Continent");

this.Property(t=>t.Region).HasColumnName("Region");

this.Property(t=>t.SurfaceArea).HasColumnName("SurfaceArea");

this.Property(t=>t.IndepYear).HasColumnName("IndepYear");

this.Property(t=>t.Population).HasColumnName("Population");

this.Property(t=>t.LifeExpectancy).HasColumnName("LifeExpectancy");

this.Property(t=>t.GNP).HasColumnName("GNP");

this.Property(t=>t.GNPOld).HasColumnName("GNPOld");

this.Property(t=>t.LocalName).HasColumnName("LocalName");

this.Property(t=>t.GovernmentForm).HasColumnName("GovernmentForm");

this.Property(t=>t.HeadOfState).HasColumnName("HeadOfState");

this.Property(t=>t.Capital).HasColumnName("Capital");

this.Property(t=>t.Code2).HasColumnName("Code2");

测试代码--延迟加载：

using(varcontext=newworldContext())

varcountry=fromdincontext.countries

whered.Name=="UnitedStates"

selectd;

varcountryUS=country.Single();

if(countryUS==null)return;

foreach(varcityincountryUS.cities)

Console.WriteLine(city.Name);

Console.Read();

测试代码--预先加载：

using(varcontext=newworldContext())

varallCountries=context.countries.Include(p=>p.cities);

foreach(varcountryinallCountries)

Console.WriteLine(country.Name);

foreach(varcityincountry.cities)

Console.WriteLine("__"+city.Name);

Console.Read();

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