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    <p>Transactions work in the manner of Amazon's SimpleDB or a sharded cluster of databases. That is to say, they are "eventually consistent" rather than guaranteed consistent.</p> <p>So when you are using transactions, the processing function may get called more than once with a local value (in some cases null if it's never been retrieved) and then again with the synced value (whatever is on the server).</p> <p>Example:</p> <pre><code>pathRef.transaction(function(curValue) { // this part is eventually consistent and may be called several times }, function(error, committed, ss) { // this part is guaranteed consistent and will match the final value set }); </code></pre> <p>This is really the mindset with which you must approach transaction anyways. You should always expect multiple calls, since the first transaction may collide with another change and be rejected. You can't use a transaction's processing method to fetch the server value (although you could read it out of the success callback).</p> <p><strong>Preventing the locally triggered event</strong></p> <p>When the transaction happens, a local event is triggered before it reaches the server for latency compensation. If the transaction fails, then the local event will be reverted (a change or remove event is triggered).</p> <p>You can use the <code>applyLocally</code> property <a href="https://www.firebase.com/docs/javascript/firebase/transaction.html" rel="noreferrer">on transactions</a> to override this behavior, which makes the local results slower but ensures that only the server value is triggered locally.</p> <pre><code>pathRef.transaction(function(curValue) { // this is still called multiple times }, function(error, committed, ss) { // this part is guaranteed consistent and will match the final value set }, // by providing a third argument of `true`, no local event // is generated with the locally cached value. true); </code></pre>
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    1. COThanks, I used transaction almost 3 days after the data inserted. So you say to use transaction first we need to check that location whether any value exists or not?
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    2. CO"Eventually persistent" has nothing to do with the length it's been on the server, just the length it has been on the client--it's not on the client until you ask for it. You do not necessarily need to check that a value exists, just accept that the function may be called multiple times and will "eventually" be called with the server value.
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Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

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