首页 \ 问答 \ 约束一对多关系(Constraint for one-to-many relationship)

约束一对多关系(Constraint for one-to-many relationship)

 我们有一个两对一的关系表。 我们希望强制执行一个约束条件，即给定的父记录至少存在一个子记录。 
 

 这可能吗？ 
 

 如果不是，你会改变架构更复杂一点来支持这种约束吗？ 如果是的话，你会怎么做？ 
 

 编辑：我正在使用SQL Server 2005 

We have a two tables with a one-to-many relationship. We would like to enforce a constraint that at least one child record exist for a given parent record. 
 

Is this possible? 
 

If not, would you change the schema a bit more complex to support such a constraint? If so how would you do it?
 

Edit: I'm using SQL Server 2005

原文：https://stackoverflow.com/questions/752023
更新时间：2022-02-07 07:02

最满意答案

 @Ash的评论引导我回答。 所以现在我有了这个T4模板 
 

<#@ template debug="true" hostSpecific="true" #>
<#@ output extension=".js" #>
<#@ Assembly Name="System.Core" #>
<#@ Assembly Name="System.Windows.Forms" #>
<#@ import namespace="System" #>
<#@ import namespace="System.IO" #>
<#@ import namespace="System.Diagnostics" #>
<#@ import namespace="System.Linq" #>
<#@ import namespace="System.Collections" #>
<#@ import namespace="System.Collections.Generic" #>
<#@ import namespace="EnvDTE" #>
<#@ include file="..\T4\Automation.ttinclude"#><#
var project = VisualStudioHelper.GetProject("MyApp.Core.Contracts");      
var contracts = GetSubClasses("MyApp.Core.Contracts.Commands.Command", project)
    .Concat(GetSubClasses("MyApp.Core.Contracts.Queries.Query", project));

#>(function(MyApp) {
    function buildContract(contract) {
        return { type: contract.constructor.type, data: ko.toJSON(contract) };
    }
    var url = "api/commandQuery";
    MyApp.cqrs = {
        sendQuery: function(query, callback) {
            $.getJSON(url, buildContract(query), callback);
        },
        sendCommand: function(command) {
            MyApp.utils.post(url, buildContract(command));
        }
    };
<#


foreach(var contract in contracts) {
        #>  
    <#
    foreach(var part in BuildNameSpace(contract)) {
        #><#= part #>
    <#
    }

    var properties = GetProperties(contract).Select(p => CamelCased(p.Name)).ToList();
    var args = string.Join(", ", properties);

    #>

    window.<#= contract.FullName #> = function(<#= args #>) {<#
    foreach(var property in properties) {#>

        this.<#= property #> = <#= property #>;<#
    }
    #>

    };
    window.<#= contract.FullName #>.type = "<#= contract.FullName #>";
<#
}
#>
})(window.MyApp = window.MyApp || {});
<#+

private static IEnumerable<string> BuildNameSpace(CodeClass @class)
{
    return BuildNameSpace(@class.Namespace.Name.Split('.'), "window", new List<string>());
}            

private static IEnumerable<string> BuildNameSpace(IEnumerable<string> @namespace, string parent, List<string> parts)
{
    var part = @namespace.FirstOrDefault();
    if (part == null) return parts;

    var current = string.Format("{0}.{1}", parent, part);
    parts.Add(string.Format("{0} = ({0} || {{}});", current));
    return BuildNameSpace(@namespace.Skip(1), current, parts);
}

public IEnumerable<CodeClass> GetSubClasses(string baseClass, Project project)
{
    return VisualStudioHelper       
        .CodeModel
        .GetAllCodeElementsOfType(project.CodeModel.CodeElements, EnvDTE.vsCMElement.vsCMElementClass, false)
        .Cast<CodeClass>()
        .Where(c => GetInheritance(c).Any(b => b.FullName == baseClass) && !c.IsAbstract)
        .ToList(); 
}


public IEnumerable<CodeClass> GetInheritance(CodeClass @class) 
{
    return GetInheritance(@class, new List<CodeClass>());
}

public IEnumerable<CodeClass> GetInheritance(CodeClass @class, List<CodeClass> collection) 
{
    foreach(CodeClass @base in @class.Bases) 
    {
        collection.Add(@base);
        GetInheritance(@base, collection);
    }

    return collection;
}

public string CamelCased(string pascalCased) {
    return pascalCased.Substring(0, 1).ToLower() + pascalCased.Substring(1);
}

public IEnumerable<CodeProperty> GetProperties(CodeClass @class)
{
    if (@class == null) 
        return new List<CodeProperty>();

    var baseProperties = GetProperties(@class.Bases.Cast<CodeClass>().FirstOrDefault());

    return baseProperties.Concat(@class
        .Members
        .Cast<CodeElement>()
        .Where(ce => ce.Kind == vsCMElement.vsCMElementProperty)
        .Cast<CodeProperty>()
        .Where(p => p.Access == vsCMAccess.vsCMAccessPublic));
    }
 #>

 

 它输出一个看起来像这样的JS，代码完成工作来自VS2012和Resharper 
 

(function(MyApp) {
    function buildContract(contract) {
        return { type: contract.constructor.type, data: ko.toJSON(contract) };
    }
    var url = "api/commandQuery";
    MyApp.cqrs = {
        sendQuery: function(query, callback) {
            $.getJSON(url, buildContract(query), callback);
        },
        sendCommand: function(command) {
            MyApp.utils.post(url, buildContract(command));
        }
    };

    window.MyApp = (window.MyApp || {});
    window.MyApp.Core = (window.MyApp.Core || {});
    window.MyApp.Core.Contracts = (window.MyApp.Core.Contracts || {});
    window.MyApp.Core.Contracts.Commands = (window.MyApp.Core.Contracts.Commands || {});

    window.MyApp.Core.Contracts.Commands.FooCommand = function(bar) {
        this.bar = bar;
    };
    window.MyApp.Core.Contracts.Commands.FooCommand.type = "MyApp.Core.Contracts.Commands.FooCommand";
})(window.MyApp = window.MyApp || {});

 

 更新代码完成无法使用旧解决方案，必须添加静态声明每个闭包单独使其正常工作 

@Ash's comment lead me to the answer. So now I have this T4 template
 

<#@ template debug="true" hostSpecific="true" #>
<#@ output extension=".js" #>
<#@ Assembly Name="System.Core" #>
<#@ Assembly Name="System.Windows.Forms" #>
<#@ import namespace="System" #>
<#@ import namespace="System.IO" #>
<#@ import namespace="System.Diagnostics" #>
<#@ import namespace="System.Linq" #>
<#@ import namespace="System.Collections" #>
<#@ import namespace="System.Collections.Generic" #>
<#@ import namespace="EnvDTE" #>
<#@ include file="..\T4\Automation.ttinclude"#><#
var project = VisualStudioHelper.GetProject("MyApp.Core.Contracts");      
var contracts = GetSubClasses("MyApp.Core.Contracts.Commands.Command", project)
    .Concat(GetSubClasses("MyApp.Core.Contracts.Queries.Query", project));

#>(function(MyApp) {
    function buildContract(contract) {
        return { type: contract.constructor.type, data: ko.toJSON(contract) };
    }
    var url = "api/commandQuery";
    MyApp.cqrs = {
        sendQuery: function(query, callback) {
            $.getJSON(url, buildContract(query), callback);
        },
        sendCommand: function(command) {
            MyApp.utils.post(url, buildContract(command));
        }
    };
<#


foreach(var contract in contracts) {
        #>  
    <#
    foreach(var part in BuildNameSpace(contract)) {
        #><#= part #>
    <#
    }

    var properties = GetProperties(contract).Select(p => CamelCased(p.Name)).ToList();
    var args = string.Join(", ", properties);

    #>

    window.<#= contract.FullName #> = function(<#= args #>) {<#
    foreach(var property in properties) {#>

        this.<#= property #> = <#= property #>;<#
    }
    #>

    };
    window.<#= contract.FullName #>.type = "<#= contract.FullName #>";
<#
}
#>
})(window.MyApp = window.MyApp || {});
<#+

private static IEnumerable<string> BuildNameSpace(CodeClass @class)
{
    return BuildNameSpace(@class.Namespace.Name.Split('.'), "window", new List<string>());
}            

private static IEnumerable<string> BuildNameSpace(IEnumerable<string> @namespace, string parent, List<string> parts)
{
    var part = @namespace.FirstOrDefault();
    if (part == null) return parts;

    var current = string.Format("{0}.{1}", parent, part);
    parts.Add(string.Format("{0} = ({0} || {{}});", current));
    return BuildNameSpace(@namespace.Skip(1), current, parts);
}

public IEnumerable<CodeClass> GetSubClasses(string baseClass, Project project)
{
    return VisualStudioHelper       
        .CodeModel
        .GetAllCodeElementsOfType(project.CodeModel.CodeElements, EnvDTE.vsCMElement.vsCMElementClass, false)
        .Cast<CodeClass>()
        .Where(c => GetInheritance(c).Any(b => b.FullName == baseClass) && !c.IsAbstract)
        .ToList(); 
}


public IEnumerable<CodeClass> GetInheritance(CodeClass @class) 
{
    return GetInheritance(@class, new List<CodeClass>());
}

public IEnumerable<CodeClass> GetInheritance(CodeClass @class, List<CodeClass> collection) 
{
    foreach(CodeClass @base in @class.Bases) 
    {
        collection.Add(@base);
        GetInheritance(@base, collection);
    }

    return collection;
}

public string CamelCased(string pascalCased) {
    return pascalCased.Substring(0, 1).ToLower() + pascalCased.Substring(1);
}

public IEnumerable<CodeProperty> GetProperties(CodeClass @class)
{
    if (@class == null) 
        return new List<CodeProperty>();

    var baseProperties = GetProperties(@class.Bases.Cast<CodeClass>().FirstOrDefault());

    return baseProperties.Concat(@class
        .Members
        .Cast<CodeElement>()
        .Where(ce => ce.Kind == vsCMElement.vsCMElementProperty)
        .Cast<CodeProperty>()
        .Where(p => p.Access == vsCMAccess.vsCMAccessPublic));
    }
 #>

 

It outputs a JS that looks like this, code completion works from VS2012 with Resharper
 

(function(MyApp) {
    function buildContract(contract) {
        return { type: contract.constructor.type, data: ko.toJSON(contract) };
    }
    var url = "api/commandQuery";
    MyApp.cqrs = {
        sendQuery: function(query, callback) {
            $.getJSON(url, buildContract(query), callback);
        },
        sendCommand: function(command) {
            MyApp.utils.post(url, buildContract(command));
        }
    };

    window.MyApp = (window.MyApp || {});
    window.MyApp.Core = (window.MyApp.Core || {});
    window.MyApp.Core.Contracts = (window.MyApp.Core.Contracts || {});
    window.MyApp.Core.Contracts.Commands = (window.MyApp.Core.Contracts.Commands || {});

    window.MyApp.Core.Contracts.Commands.FooCommand = function(bar) {
        this.bar = bar;
    };
    window.MyApp.Core.Contracts.Commands.FooCommand.type = "MyApp.Core.Contracts.Commands.FooCommand";
})(window.MyApp = window.MyApp || {});

 

Update Code completion didnt work with old solution, had to add the staticly declare each closure seperate for it to work correctly

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