/// <summary>
/// Create a <see cref="LambdaExpression"/> such as: Expression{Func{Sales, keyType}} projectionLambda = s => new KeyType(Amount = s.Amount, Id=s.Id).
/// </summary>
/// <param name="selectStatements">The selected statements creating the key of the group-by operation.</param>
/// <param name="keyType">The type of the key of the group-by operation.</param>
/// <param name="propertiesToGroupByExpressions">List of expressions to the properties to group by.</param>
/// <returns><see cref="LambdaExpression"/>.</returns>
private LambdaExpression GetGroupByProjectionLambda(string[] selectStatements, Type keyType, LambdaExpression[] propertiesToGroupByExpressions)
{
Contract.Assert(keyType != null);
Contract.Assert(selectStatements != null && selectStatements.Any());
ParameterExpression entityParam;
if (propertiesToGroupByExpressions != null && propertiesToGroupByExpressions.Any())
{
entityParam = propertiesToGroupByExpressions.First().Parameters.First();
}
else
{
entityParam = Expression.Parameter(this.Context.ElementClrType, "e");
}
var bindings = new List <MemberAssignment>();
for (int i = 0; i < selectStatements.Length; i++)
{
var statement = selectStatements[i];
Expression selectedProperyExpression = null;
if (propertiesToGroupByExpressions != null)
{
selectedProperyExpression = propertiesToGroupByExpressions[i].Body;
}
string samplingMethod, alias, samplingProperty;
GroupByImplementation.GetSamplingMethod(statement, out samplingMethod, out alias, out samplingProperty);
if (samplingMethod == null)
{
var prop = statement;
if (prop.Contains('/'))
{
prop = statement.Substring(0, prop.IndexOf('/'));
}
prop = prop.TrimMethodCall().Split(' ').First();
var mi = keyType.GetMember(prop).First();
bindings.Add(Expression.Bind(mi, ApplyImplementationBase.GetPropertyExpression(keyType, statement, entityParam, selectedProperyExpression)));
}
else
{
string prop = alias;
if (statement.Contains('/'))
{
prop = statement.Substring(0, statement.IndexOf('/'));
}
var mi = keyType.GetMember(prop).First();
var propertyType = GetPropertyInfo(this.Context.ElementClrType, statement).Last().PropertyType;
var implementation = SamplingMethodsImplementations.GetAggregationImplementation(samplingMethod);
MethodInfo method = implementation.GetSamplingProcessingMethod(propertyType);
var aggregationParamsExpressions = GetAggregationArgumentsExpressions(samplingMethod, method);
bindings.Add(Expression.Bind(mi, ApplyImplementationBase.GetComputedPropertyExpression(keyType, statement, entityParam, method, selectedProperyExpression, aggregationParamsExpressions)));
}
}
var body = Expression.MemberInit(Expression.New(keyType), bindings);
return(Expression.Lambda(body, entityParam));
}
