[SalesForce] Apex Maps and SOQL queries

I am trying to put the values from my SOQL query into a map.

This is my example:
I have a custom object "disease__c" and a custom object "patient__c". They are a master-detail relationship where disease__c is the master object.

My query is like this:

SELECT Email__c, diseaseR__r.Name FROM patient__c;

Like this I will get all the email addresses of patients linked to a disease.

So, what I now need to do is to send an email to all patients that have a certain disease, i.e. all patients that have Rubella will receive an email saying "You have Rubella" (btw – I am learning Force.com development, this is not a real application ;))

This is what I have done:

Map<String, String> email_disease_pairs = new Map <String, String> ();
email_disease_pairs = [SELECT Email__c, diseaseR__r.Name FROM patient__c];

Unfortunately I get the following error:

Save error: list must have exactly 1 type argument

I am not sure what this means?

Any help would be appreciated!

Best Answer

Check this:

Map<Id, Set<String>> emailDiseaseMap = new Map <Id, Set<String>> ();

for(Patient__c patient : [  SELECT Email__c, Diseaser__c 
                            FROM Patient__c]){
    if(!emailDiseaseMap.containsKey(patient.Diseaser__c)){
        emailDiseaseMap.put(patient.Diseaser__c , new Set<String>());
    }
    emailDiseaseMap.get(patient.Diseaser__c).add(patient.Email__c);
}

I've make some changes in your code:

Map type is change to Map<Id, Set<String>> because - Id of parent is unique value and id could happen that you have 2 record with same name - and I don't think you want this. I also used Set<String> to keep all unique email adresses for paarent.

Related Solutions

[SalesForce] Iterating over a map (Apex)

These methods are available for all maps.

So one way to code it is to use a keySet() method of the Map.
Firstly you will get all Id's (keys) from the map and then will iterate over that set of keys. Based on the key you can then get a corresponding set of emails:

for (Id key : emailDiseaseMap.keySet()) {
    // The "key" variable is also available inside the loop
    List<String> toAddresses = emailDiseaseMap.get(key);
    // ... emailing logic
}

[SalesForce] Multiple SOQL queries in single request

This is a perfect example of where it makes sense to use SOSL, rather than SOQL. The following SOSL search query, made using the Partner WSDL from Java (adapted from this example, which also includes source code examples for C#), should do the trick:

    String email = "a@a.com";

    // (OPTIONAL, depending on how sanitized your inputs are already)
    // Escape single quotes that might occur in the string to prevent SOSL Injection
    // http://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/StringEscapeUtils.html#escapeEcmaScript(java.lang.String)
    email = StringEscapeUtils.escapeEcmaScript(email);

    String soslQuery = 
        "FIND {" + email + "} IN Email FIELDS " +
        "RETURNING " +
        "Lead(Id,Email), Contact(Id,Email)";
    // Perform SOSL query
    SearchResult sResult = partnerConnection.search(soslQuery);
    // Get the records returned by the search result
    SearchRecord[] records = sResult.getSearchRecords();
    // Create lists of objects to hold search result records
    List<SObject> contacts = new ArrayList<SObject>();
    List<SObject> leads = new ArrayList<SObject>();

    // Iterate through the search result records
    // and store the records in their corresponding lists
    // based on record type.
    if (records != null && records.length > 0) {
      for (int i = 0; i < records.length; i++){
        SObject record = records[i].getRecord();
        if (record.getType().toLowerCase().equals("contact")) {
          contacts.add(record);
        } else if (record.getType().toLowerCase().equals("lead")){
          leads.add(record);
        }
      }

Why is SOSL appropriate here, rather than SOQL?

A SOSL search here can be made using the Partner WSDL with only a single API call, whereas a SOQL query to achieve the same result would require 2 API calls, burning through an organization's daily limits twice as fast.
SOSL can return records of multiple types of SObjects all at once --- SOQL cannot.

If you weren't doing an exact text search against Contact and Lead, I would also add that SOSL would be essential for doing this sort of search in an organization with any significant data volume, since Email fields are ordinarily not indexed, and so a SOQL query against a non-custom-indexed Email field on any Custom Object would require a full table scan, rendering your query completely useless in an org with lots and lots of records. But because you are doing an exact text match search against against the Email field on Contact and Lead, you would technically be fine with SOQL as far as performance goes, because the Email field is indexed on Contact and Lead. Why do I mention this here if it doesn't apply? Because it's good to get in the habit of using the right tools for the right scenario, and to know why they're the right tools. SOSL is perfect for this type of search query.

There is one gotcha to watch out for, though --- SOSL's indexes do not update immediately. In my experience, it takes at least 30 seconds for the SOSL indexes to update after records are modified. So if, for example, a user just created a new Contact, and then ran this SOSL query 10 seconds later, that Contact record would not be returned in the search. If this is unacceptable for your situation (which I doubt it is), you'd have to use SOQL for this scenario.

Best Answer

Related Solutions

[SalesForce] Iterating over a map (Apex)

[SalesForce] Multiple SOQL queries in single request

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