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2011-01-12T15:14:51.157
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Try this: <pre><code>public class Account : Base { ... public override Expression<Func<T, bool>> MustNotAlreadyExist() { return (b => b.Name == name && b.AccountCode == accountCode).Any(); } ... } </code></pre> The Any() method will return true if any record matches the predicate. It could be argued that it is outside the responsibility of the repository to check for presence of a record before saving. UPDATE: There is a great article on CodeProject that describes a generic Repository for Entity Framework: <a href="http://www.codeproject.com/KB/database/ImplRepositoryPatternEF.aspx" rel="nofollow">http://www.codeproject.com/KB/database/ImplRepositoryPatternEF.aspx</a> This could be applied to a non-Entity Framework data context. Here is an excerpt that provides a very flexible method for checking for an existing value by accepting the name of a field, a value, and a key value. You can apply this to any Entity type and use it to check for the presence of an entity before attempting a save. <pre><code>/// <summary> /// Check if value of specific field is already exist /// </summary> /// <typeparam name="E"></typeparam> /// <param name="fieldName">name of the Field</param> /// <param name="fieldValue">Field value</param> /// <param name="key">Primary key value</param> /// <returns>True or False</returns> public bool TrySameValueExist(string fieldName, object fieldValue, string key) { // First we define the parameter that we are going to use the clause. var xParam = Expression.Parameter(typeof(E), typeof(E).Name); MemberExpression leftExprFieldCheck = MemberExpression.Property(xParam, fieldName); Expression rightExprFieldCheck = Expression.Constant(fieldValue); BinaryExpression binaryExprFieldCheck = MemberExpression.Equal(leftExprFieldCheck, rightExprFieldCheck); MemberExpression leftExprKeyCheck = MemberExpression.Property(xParam, this._KeyProperty); Expression rightExprKeyCheck = Expression.Constant(key); BinaryExpression binaryExprKeyCheck = MemberExpression.NotEqual(leftExprKeyCheck, rightExprKeyCheck); BinaryExpression finalBinaryExpr = Expression.And(binaryExprFieldCheck, binaryExprKeyCheck); //Create Lambda Expression for the selection Expression<Func<E, bool>> lambdaExpr = Expression.Lambda<Func<E, bool>>(finalBinaryExpr, new ParameterExpression[] { xParam }); //Searching .... return ((IRepository<E, C>)this).TryEntity(new Specification<E>(lambdaExpr)); } /// <summary> /// Check if Entities exist with Condition /// </summary> /// <param name="selectExpression">Selection Condition</param> /// <returns>True or False</returns> public bool TryEntity(ISpecification<E> selectSpec) { return _ctx.CreateQuery<E>("[" + typeof(E).Name + "]").Any<E> (selectSpec.EvalPredicate); } </code></pre>
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1. POWhen using a repository is it possible for a type to return a Func that the repository uses to test for existing entities?
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1. USDave Swersky
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1. COThis doesn't compile ... what I want to return from this method is an Expression (or Func) that I can pass into the GetAll().Any(...) call.
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2. CO@Scott: See update.
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